Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1107 insertions, 0 deletions

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
new file mode 100644
index 000000000..ae9e806a1
--- /dev/null
+++ b/arch/x86/kernel/uprobes.c
@@ -0,0 +1,1107 @@
+/*
+ * User-space Probes (UProbes) for x86
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2008-2011
+ * Authors:
+ *	Srikar Dronamraju
+ *	Jim Keniston
+ */
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/ptrace.h>
+#include <linux/uprobes.h>
+#include <linux/uaccess.h>
+
+#include <linux/kdebug.h>
+#include <asm/processor.h>
+#include <asm/insn.h>
+#include <asm/mmu_context.h>
+
+/* Post-execution fixups. */
+
+/* Adjust IP back to vicinity of actual insn */
+#define UPROBE_FIX_IP		0x01
+
+/* Adjust the return address of a call insn */
+#define UPROBE_FIX_CALL		0x02
+
+/* Instruction will modify TF, don't change it */
+#define UPROBE_FIX_SETF		0x04
+
+#define UPROBE_FIX_RIP_SI	0x08
+#define UPROBE_FIX_RIP_DI	0x10
+#define UPROBE_FIX_RIP_BX	0x20
+#define UPROBE_FIX_RIP_MASK	\
+	(UPROBE_FIX_RIP_SI | UPROBE_FIX_RIP_DI | UPROBE_FIX_RIP_BX)
+
+#define	UPROBE_TRAP_NR		UINT_MAX
+
+/* Adaptations for mhiramat x86 decoder v14. */
+#define OPCODE1(insn)		((insn)->opcode.bytes[0])
+#define OPCODE2(insn)		((insn)->opcode.bytes[1])
+#define OPCODE3(insn)		((insn)->opcode.bytes[2])
+#define MODRM_REG(insn)		X86_MODRM_REG((insn)->modrm.value)
+
+#define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\
+	(((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
+	  (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
+	  (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
+	  (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
+	 << (row % 32))
+
+/*
+ * Good-instruction tables for 32-bit apps.  This is non-const and volatile
+ * to keep gcc from statically optimizing it out, as variable_test_bit makes
+ * some versions of gcc to think only *(unsigned long*) is used.
+ *
+ * Opcodes we'll probably never support:
+ * 6c-6f - ins,outs. SEGVs if used in userspace
+ * e4-e7 - in,out imm. SEGVs if used in userspace
+ * ec-ef - in,out acc. SEGVs if used in userspace
+ * cc - int3. SIGTRAP if used in userspace
+ * ce - into. Not used in userspace - no kernel support to make it useful. SEGVs
+ *	(why we support bound (62) then? it's similar, and similarly unused...)
+ * f1 - int1. SIGTRAP if used in userspace
+ * f4 - hlt. SEGVs if used in userspace
+ * fa - cli. SEGVs if used in userspace
+ * fb - sti. SEGVs if used in userspace
+ *
+ * Opcodes which need some work to be supported:
+ * 07,17,1f - pop es/ss/ds
+ *	Normally not used in userspace, but would execute if used.
+ *	Can cause GP or stack exception if tries to load wrong segment descriptor.
+ *	We hesitate to run them under single step since kernel's handling
+ *	of userspace single-stepping (TF flag) is fragile.
+ *	We can easily refuse to support push es/cs/ss/ds (06/0e/16/1e)
+ *	on the same grounds that they are never used.
+ * cd - int N.
+ *	Used by userspace for "int 80" syscall entry. (Other "int N"
+ *	cause GP -> SEGV since their IDT gates don't allow calls from CPL 3).
+ *	Not supported since kernel's handling of userspace single-stepping
+ *	(TF flag) is fragile.
+ * cf - iret. Normally not used in userspace. Doesn't SEGV unless arguments are bad
+ */
+#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
+static volatile u32 good_insns_32[256 / 32] = {
+	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
+	/*      ----------------------------------------------         */
+	W(0x00, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* 00 */
+	W(0x10, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) , /* 10 */
+	W(0x20, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 20 */
+	W(0x30, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 30 */
+	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
+	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
+	W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
+	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */
+	W(0x80, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
+	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
+	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */
+	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
+	W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
+	W(0xd0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
+	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* e0 */
+	W(0xf0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
+	/*      ----------------------------------------------         */
+	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
+};
+#else
+#define good_insns_32	NULL
+#endif
+
+/* Good-instruction tables for 64-bit apps.
+ *
+ * Genuinely invalid opcodes:
+ * 06,07 - formerly push/pop es
+ * 0e - formerly push cs
+ * 16,17 - formerly push/pop ss
+ * 1e,1f - formerly push/pop ds
+ * 27,2f,37,3f - formerly daa/das/aaa/aas
+ * 60,61 - formerly pusha/popa
+ * 62 - formerly bound. EVEX prefix for AVX512 (not yet supported)
+ * 82 - formerly redundant encoding of Group1
+ * 9a - formerly call seg:ofs
+ * ce - formerly into
+ * d4,d5 - formerly aam/aad
+ * d6 - formerly undocumented salc
+ * ea - formerly jmp seg:ofs
+ *
+ * Opcodes we'll probably never support:
+ * 6c-6f - ins,outs. SEGVs if used in userspace
+ * e4-e7 - in,out imm. SEGVs if used in userspace
+ * ec-ef - in,out acc. SEGVs if used in userspace
+ * cc - int3. SIGTRAP if used in userspace
+ * f1 - int1. SIGTRAP if used in userspace
+ * f4 - hlt. SEGVs if used in userspace
+ * fa - cli. SEGVs if used in userspace
+ * fb - sti. SEGVs if used in userspace
+ *
+ * Opcodes which need some work to be supported:
+ * cd - int N.
+ *	Used by userspace for "int 80" syscall entry. (Other "int N"
+ *	cause GP -> SEGV since their IDT gates don't allow calls from CPL 3).
+ *	Not supported since kernel's handling of userspace single-stepping
+ *	(TF flag) is fragile.
+ * cf - iret. Normally not used in userspace. Doesn't SEGV unless arguments are bad
+ */
+#if defined(CONFIG_X86_64)
+static volatile u32 good_insns_64[256 / 32] = {
+	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
+	/*      ----------------------------------------------         */
+	W(0x00, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1) | /* 00 */
+	W(0x10, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 10 */
+	W(0x20, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) | /* 20 */
+	W(0x30, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) , /* 30 */
+	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
+	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
+	W(0x60, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
+	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */
+	W(0x80, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
+	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1) , /* 90 */
+	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */
+	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
+	W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
+	W(0xd0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
+	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0) | /* e0 */
+	W(0xf0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
+	/*      ----------------------------------------------         */
+	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
+};
+#else
+#define good_insns_64	NULL
+#endif
+
+/* Using this for both 64-bit and 32-bit apps.
+ * Opcodes we don't support:
+ * 0f 00 - SLDT/STR/LLDT/LTR/VERR/VERW/-/- group. System insns
+ * 0f 01 - SGDT/SIDT/LGDT/LIDT/SMSW/-/LMSW/INVLPG group.
+ *	Also encodes tons of other system insns if mod=11.
+ *	Some are in fact non-system: xend, xtest, rdtscp, maybe more
+ * 0f 05 - syscall
+ * 0f 06 - clts (CPL0 insn)
+ * 0f 07 - sysret
+ * 0f 08 - invd (CPL0 insn)
+ * 0f 09 - wbinvd (CPL0 insn)
+ * 0f 0b - ud2
+ * 0f 30 - wrmsr (CPL0 insn) (then why rdmsr is allowed, it's also CPL0 insn?)
+ * 0f 34 - sysenter
+ * 0f 35 - sysexit
+ * 0f 37 - getsec
+ * 0f 78 - vmread (Intel VMX. CPL0 insn)
+ * 0f 79 - vmwrite (Intel VMX. CPL0 insn)
+ *	Note: with prefixes, these two opcodes are
+ *	extrq/insertq/AVX512 convert vector ops.
+ * 0f ae - group15: [f]xsave,[f]xrstor,[v]{ld,st}mxcsr,clflush[opt],
+ *	{rd,wr}{fs,gs}base,{s,l,m}fence.
+ *	Why? They are all user-executable.
+ */
+static volatile u32 good_2byte_insns[256 / 32] = {
+	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
+	/*      ----------------------------------------------         */
+	W(0x00, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1) | /* 00 */
+	W(0x10, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 10 */
+	W(0x20, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 20 */
+	W(0x30, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1) , /* 30 */
+	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
+	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
+	W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 60 */
+	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1) , /* 70 */
+	W(0x80, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
+	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
+	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1) | /* a0 */
+	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
+	W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* c0 */
+	W(0xd0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
+	W(0xe0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* e0 */
+	W(0xf0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)   /* f0 */
+	/*      ----------------------------------------------         */
+	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
+};
+#undef W
+
+/*
+ * opcodes we may need to refine support for:
+ *
+ *  0f - 2-byte instructions: For many of these instructions, the validity
+ *  depends on the prefix and/or the reg field.  On such instructions, we
+ *  just consider the opcode combination valid if it corresponds to any
+ *  valid instruction.
+ *
+ *  8f - Group 1 - only reg = 0 is OK
+ *  c6-c7 - Group 11 - only reg = 0 is OK
+ *  d9-df - fpu insns with some illegal encodings
+ *  f2, f3 - repnz, repz prefixes.  These are also the first byte for
+ *  certain floating-point instructions, such as addsd.
+ *
+ *  fe - Group 4 - only reg = 0 or 1 is OK
+ *  ff - Group 5 - only reg = 0-6 is OK
+ *
+ * others -- Do we need to support these?
+ *
+ *  0f - (floating-point?) prefetch instructions
+ *  07, 17, 1f - pop es, pop ss, pop ds
+ *  26, 2e, 36, 3e - es:, cs:, ss:, ds: segment prefixes --
+ *	but 64 and 65 (fs: and gs:) seem to be used, so we support them
+ *  67 - addr16 prefix
+ *  ce - into
+ *  f0 - lock prefix
+ */
+
+/*
+ * TODO:
+ * - Where necessary, examine the modrm byte and allow only valid instructions
+ * in the different Groups and fpu instructions.
+ */
+
+static bool is_prefix_bad(struct insn *insn)
+{
+	insn_byte_t p;
+	int i;
+
+	for_each_insn_prefix(insn, i, p) {
+		insn_attr_t attr;
+
+		attr = inat_get_opcode_attribute(p);
+		switch (attr) {
+		case INAT_MAKE_PREFIX(INAT_PFX_ES):
+		case INAT_MAKE_PREFIX(INAT_PFX_CS):
+		case INAT_MAKE_PREFIX(INAT_PFX_DS):
+		case INAT_MAKE_PREFIX(INAT_PFX_SS):
+		case INAT_MAKE_PREFIX(INAT_PFX_LOCK):
+			return true;
+		}
+	}
+	return false;
+}
+
+static int uprobe_init_insn(struct arch_uprobe *auprobe, struct insn *insn, bool x86_64)
+{
+	u32 volatile *good_insns;
+
+	insn_init(insn, auprobe->insn, sizeof(auprobe->insn), x86_64);
+	/* has the side-effect of processing the entire instruction */
+	insn_get_length(insn);
+	if (!insn_complete(insn))
+		return -ENOEXEC;
+
+	if (is_prefix_bad(insn))
+		return -ENOTSUPP;
+
+	/* We should not singlestep on the exception masking instructions */
+	if (insn_masking_exception(insn))
+		return -ENOTSUPP;
+
+	if (x86_64)
+		good_insns = good_insns_64;
+	else
+		good_insns = good_insns_32;
+
+	if (test_bit(OPCODE1(insn), (unsigned long *)good_insns))
+		return 0;
+
+	if (insn->opcode.nbytes == 2) {
+		if (test_bit(OPCODE2(insn), (unsigned long *)good_2byte_insns))
+			return 0;
+	}
+
+	return -ENOTSUPP;
+}
+
+#ifdef CONFIG_X86_64
+/*
+ * If arch_uprobe->insn doesn't use rip-relative addressing, return
+ * immediately.  Otherwise, rewrite the instruction so that it accesses
+ * its memory operand indirectly through a scratch register.  Set
+ * defparam->fixups accordingly. (The contents of the scratch register
+ * will be saved before we single-step the modified instruction,
+ * and restored afterward).
+ *
+ * We do this because a rip-relative instruction can access only a
+ * relatively small area (+/- 2 GB from the instruction), and the XOL
+ * area typically lies beyond that area.  At least for instructions
+ * that store to memory, we can't execute the original instruction
+ * and "fix things up" later, because the misdirected store could be
+ * disastrous.
+ *
+ * Some useful facts about rip-relative instructions:
+ *
+ *  - There's always a modrm byte with bit layout "00 reg 101".
+ *  - There's never a SIB byte.
+ *  - The displacement is always 4 bytes.
+ *  - REX.B=1 bit in REX prefix, which normally extends r/m field,
+ *    has no effect on rip-relative mode. It doesn't make modrm byte
+ *    with r/m=101 refer to register 1101 = R13.
+ */
+static void riprel_analyze(struct arch_uprobe *auprobe, struct insn *insn)
+{
+	u8 *cursor;
+	u8 reg;
+	u8 reg2;
+
+	if (!insn_rip_relative(insn))
+		return;
+
+	/*
+	 * insn_rip_relative() would have decoded rex_prefix, vex_prefix, modrm.
+	 * Clear REX.b bit (extension of MODRM.rm field):
+	 * we want to encode low numbered reg, not r8+.
+	 */
+	if (insn->rex_prefix.nbytes) {
+		cursor = auprobe->insn + insn_offset_rex_prefix(insn);
+		/* REX byte has 0100wrxb layout, clearing REX.b bit */
+		*cursor &= 0xfe;
+	}
+	/*
+	 * Similar treatment for VEX3/EVEX prefix.
+	 * TODO: add XOP treatment when insn decoder supports them
+	 */
+	if (insn->vex_prefix.nbytes >= 3) {
+		/*
+		 * vex2:     c5    rvvvvLpp   (has no b bit)
+		 * vex3/xop: c4/8f rxbmmmmm wvvvvLpp
+		 * evex:     62    rxbR00mm wvvvv1pp zllBVaaa
+		 * Setting VEX3.b (setting because it has inverted meaning).
+		 * Setting EVEX.x since (in non-SIB encoding) EVEX.x
+		 * is the 4th bit of MODRM.rm, and needs the same treatment.
+		 * For VEX3-encoded insns, VEX3.x value has no effect in
+		 * non-SIB encoding, the change is superfluous but harmless.
+		 */
+		cursor = auprobe->insn + insn_offset_vex_prefix(insn) + 1;
+		*cursor |= 0x60;
+	}
+
+	/*
+	 * Convert from rip-relative addressing to register-relative addressing
+	 * via a scratch register.
+	 *
+	 * This is tricky since there are insns with modrm byte
+	 * which also use registers not encoded in modrm byte:
+	 * [i]div/[i]mul: implicitly use dx:ax
+	 * shift ops: implicitly use cx
+	 * cmpxchg: implicitly uses ax
+	 * cmpxchg8/16b: implicitly uses dx:ax and bx:cx
+	 *   Encoding: 0f c7/1 modrm
+	 *   The code below thinks that reg=1 (cx), chooses si as scratch.
+	 * mulx: implicitly uses dx: mulx r/m,r1,r2 does r1:r2 = dx * r/m.
+	 *   First appeared in Haswell (BMI2 insn). It is vex-encoded.
+	 *   Example where none of bx,cx,dx can be used as scratch reg:
+	 *   c4 e2 63 f6 0d disp32   mulx disp32(%rip),%ebx,%ecx
+	 * [v]pcmpistri: implicitly uses cx, xmm0
+	 * [v]pcmpistrm: implicitly uses xmm0
+	 * [v]pcmpestri: implicitly uses ax, dx, cx, xmm0
+	 * [v]pcmpestrm: implicitly uses ax, dx, xmm0
+	 *   Evil SSE4.2 string comparison ops from hell.
+	 * maskmovq/[v]maskmovdqu: implicitly uses (ds:rdi) as destination.
+	 *   Encoding: 0f f7 modrm, 66 0f f7 modrm, vex-encoded: c5 f9 f7 modrm.
+	 *   Store op1, byte-masked by op2 msb's in each byte, to (ds:rdi).
+	 *   AMD says it has no 3-operand form (vex.vvvv must be 1111)
+	 *   and that it can have only register operands, not mem
+	 *   (its modrm byte must have mode=11).
+	 *   If these restrictions will ever be lifted,
+	 *   we'll need code to prevent selection of di as scratch reg!
+	 *
+	 * Summary: I don't know any insns with modrm byte which
+	 * use SI register implicitly. DI register is used only
+	 * by one insn (maskmovq) and BX register is used
+	 * only by one too (cmpxchg8b).
+	 * BP is stack-segment based (may be a problem?).
+	 * AX, DX, CX are off-limits (many implicit users).
+	 * SP is unusable (it's stack pointer - think about "pop mem";
+	 * also, rsp+disp32 needs sib encoding -> insn length change).
+	 */
+
+	reg = MODRM_REG(insn);	/* Fetch modrm.reg */
+	reg2 = 0xff;		/* Fetch vex.vvvv */
+	if (insn->vex_prefix.nbytes)
+		reg2 = insn->vex_prefix.bytes[2];
+	/*
+	 * TODO: add XOP vvvv reading.
+	 *
+	 * vex.vvvv field is in bits 6-3, bits are inverted.
+	 * But in 32-bit mode, high-order bit may be ignored.
+	 * Therefore, let's consider only 3 low-order bits.
+	 */
+	reg2 = ((reg2 >> 3) & 0x7) ^ 0x7;
+	/*
+	 * Register numbering is ax,cx,dx,bx, sp,bp,si,di, r8..r15.
+	 *
+	 * Choose scratch reg. Order is important: must not select bx
+	 * if we can use si (cmpxchg8b case!)
+	 */
+	if (reg != 6 && reg2 != 6) {
+		reg2 = 6;
+		auprobe->defparam.fixups |= UPROBE_FIX_RIP_SI;
+	} else if (reg != 7 && reg2 != 7) {
+		reg2 = 7;
+		auprobe->defparam.fixups |= UPROBE_FIX_RIP_DI;
+		/* TODO (paranoia): force maskmovq to not use di */
+	} else {
+		reg2 = 3;
+		auprobe->defparam.fixups |= UPROBE_FIX_RIP_BX;
+	}
+	/*
+	 * Point cursor at the modrm byte.  The next 4 bytes are the
+	 * displacement.  Beyond the displacement, for some instructions,
+	 * is the immediate operand.
+	 */
+	cursor = auprobe->insn + insn_offset_modrm(insn);
+	/*
+	 * Change modrm from "00 reg 101" to "10 reg reg2". Example:
+	 * 89 05 disp32  mov %eax,disp32(%rip) becomes
+	 * 89 86 disp32  mov %eax,disp32(%rsi)
+	 */
+	*cursor = 0x80 | (reg << 3) | reg2;
+}
+
+static inline unsigned long *
+scratch_reg(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	if (auprobe->defparam.fixups & UPROBE_FIX_RIP_SI)
+		return &regs->si;
+	if (auprobe->defparam.fixups & UPROBE_FIX_RIP_DI)
+		return &regs->di;
+	return &regs->bx;
+}
+
+/*
+ * If we're emulating a rip-relative instruction, save the contents
+ * of the scratch register and store the target address in that register.
+ */
+static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	if (auprobe->defparam.fixups & UPROBE_FIX_RIP_MASK) {
+		struct uprobe_task *utask = current->utask;
+		unsigned long *sr = scratch_reg(auprobe, regs);
+
+		utask->autask.saved_scratch_register = *sr;
+		*sr = utask->vaddr + auprobe->defparam.ilen;
+	}
+}
+
+static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	if (auprobe->defparam.fixups & UPROBE_FIX_RIP_MASK) {
+		struct uprobe_task *utask = current->utask;
+		unsigned long *sr = scratch_reg(auprobe, regs);
+
+		*sr = utask->autask.saved_scratch_register;
+	}
+}
+#else /* 32-bit: */
+/*
+ * No RIP-relative addressing on 32-bit
+ */
+static void riprel_analyze(struct arch_uprobe *auprobe, struct insn *insn)
+{
+}
+static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+}
+static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+}
+#endif /* CONFIG_X86_64 */
+
+struct uprobe_xol_ops {
+	bool	(*emulate)(struct arch_uprobe *, struct pt_regs *);
+	int	(*pre_xol)(struct arch_uprobe *, struct pt_regs *);
+	int	(*post_xol)(struct arch_uprobe *, struct pt_regs *);
+	void	(*abort)(struct arch_uprobe *, struct pt_regs *);
+};
+
+static inline int sizeof_long(struct pt_regs *regs)
+{
+	/*
+	 * Check registers for mode as in_xxx_syscall() does not apply here.
+	 */
+	return user_64bit_mode(regs) ? 8 : 4;
+}
+
+static int default_pre_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	riprel_pre_xol(auprobe, regs);
+	return 0;
+}
+
+static int emulate_push_stack(struct pt_regs *regs, unsigned long val)
+{
+	unsigned long new_sp = regs->sp - sizeof_long(regs);
+
+	if (copy_to_user((void __user *)new_sp, &val, sizeof_long(regs)))
+		return -EFAULT;
+
+	regs->sp = new_sp;
+	return 0;
+}
+
+/*
+ * We have to fix things up as follows:
+ *
+ * Typically, the new ip is relative to the copied instruction.  We need
+ * to make it relative to the original instruction (FIX_IP).  Exceptions
+ * are return instructions and absolute or indirect jump or call instructions.
+ *
+ * If the single-stepped instruction was a call, the return address that
+ * is atop the stack is the address following the copied instruction.  We
+ * need to make it the address following the original instruction (FIX_CALL).
+ *
+ * If the original instruction was a rip-relative instruction such as
+ * "movl %edx,0xnnnn(%rip)", we have instead executed an equivalent
+ * instruction using a scratch register -- e.g., "movl %edx,0xnnnn(%rsi)".
+ * We need to restore the contents of the scratch register
+ * (FIX_RIP_reg).
+ */
+static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	riprel_post_xol(auprobe, regs);
+	if (auprobe->defparam.fixups & UPROBE_FIX_IP) {
+		long correction = utask->vaddr - utask->xol_vaddr;
+		regs->ip += correction;
+	} else if (auprobe->defparam.fixups & UPROBE_FIX_CALL) {
+		regs->sp += sizeof_long(regs); /* Pop incorrect return address */
+		if (emulate_push_stack(regs, utask->vaddr + auprobe->defparam.ilen))
+			return -ERESTART;
+	}
+	/* popf; tell the caller to not touch TF */
+	if (auprobe->defparam.fixups & UPROBE_FIX_SETF)
+		utask->autask.saved_tf = true;
+
+	return 0;
+}
+
+static void default_abort_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	riprel_post_xol(auprobe, regs);
+}
+
+static const struct uprobe_xol_ops default_xol_ops = {
+	.pre_xol  = default_pre_xol_op,
+	.post_xol = default_post_xol_op,
+	.abort	  = default_abort_op,
+};
+
+static bool branch_is_call(struct arch_uprobe *auprobe)
+{
+	return auprobe->branch.opc1 == 0xe8;
+}
+
+#define CASE_COND					\
+	COND(70, 71, XF(OF))				\
+	COND(72, 73, XF(CF))				\
+	COND(74, 75, XF(ZF))				\
+	COND(78, 79, XF(SF))				\
+	COND(7a, 7b, XF(PF))				\
+	COND(76, 77, XF(CF) || XF(ZF))			\
+	COND(7c, 7d, XF(SF) != XF(OF))			\
+	COND(7e, 7f, XF(ZF) || XF(SF) != XF(OF))
+
+#define COND(op_y, op_n, expr)				\
+	case 0x ## op_y: DO((expr) != 0)		\
+	case 0x ## op_n: DO((expr) == 0)
+
+#define XF(xf)	(!!(flags & X86_EFLAGS_ ## xf))
+
+static bool is_cond_jmp_opcode(u8 opcode)
+{
+	switch (opcode) {
+	#define DO(expr)	\
+		return true;
+	CASE_COND
+	#undef	DO
+
+	default:
+		return false;
+	}
+}
+
+static bool check_jmp_cond(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	unsigned long flags = regs->flags;
+
+	switch (auprobe->branch.opc1) {
+	#define DO(expr)	\
+		return expr;
+	CASE_COND
+	#undef	DO
+
+	default:	/* not a conditional jmp */
+		return true;
+	}
+}
+
+#undef	XF
+#undef	COND
+#undef	CASE_COND
+
+static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	unsigned long new_ip = regs->ip += auprobe->branch.ilen;
+	unsigned long offs = (long)auprobe->branch.offs;
+
+	if (branch_is_call(auprobe)) {
+		/*
+		 * If it fails we execute this (mangled, see the comment in
+		 * branch_clear_offset) insn out-of-line. In the likely case
+		 * this should trigger the trap, and the probed application
+		 * should die or restart the same insn after it handles the
+		 * signal, arch_uprobe_post_xol() won't be even called.
+		 *
+		 * But there is corner case, see the comment in ->post_xol().
+		 */
+		if (emulate_push_stack(regs, new_ip))
+			return false;
+	} else if (!check_jmp_cond(auprobe, regs)) {
+		offs = 0;
+	}
+
+	regs->ip = new_ip + offs;
+	return true;
+}
+
+static bool push_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	unsigned long *src_ptr = (void *)regs + auprobe->push.reg_offset;
+
+	if (emulate_push_stack(regs, *src_ptr))
+		return false;
+	regs->ip += auprobe->push.ilen;
+	return true;
+}
+
+static int branch_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	BUG_ON(!branch_is_call(auprobe));
+	/*
+	 * We can only get here if branch_emulate_op() failed to push the ret
+	 * address _and_ another thread expanded our stack before the (mangled)
+	 * "call" insn was executed out-of-line. Just restore ->sp and restart.
+	 * We could also restore ->ip and try to call branch_emulate_op() again.
+	 */
+	regs->sp += sizeof_long(regs);
+	return -ERESTART;
+}
+
+static void branch_clear_offset(struct arch_uprobe *auprobe, struct insn *insn)
+{
+	/*
+	 * Turn this insn into "call 1f; 1:", this is what we will execute
+	 * out-of-line if ->emulate() fails. We only need this to generate
+	 * a trap, so that the probed task receives the correct signal with
+	 * the properly filled siginfo.
+	 *
+	 * But see the comment in ->post_xol(), in the unlikely case it can
+	 * succeed. So we need to ensure that the new ->ip can not fall into
+	 * the non-canonical area and trigger #GP.
+	 *
+	 * We could turn it into (say) "pushf", but then we would need to
+	 * divorce ->insn[] and ->ixol[]. We need to preserve the 1st byte
+	 * of ->insn[] for set_orig_insn().
+	 */
+	memset(auprobe->insn + insn_offset_immediate(insn),
+		0, insn->immediate.nbytes);
+}
+
+static const struct uprobe_xol_ops branch_xol_ops = {
+	.emulate  = branch_emulate_op,
+	.post_xol = branch_post_xol_op,
+};
+
+static const struct uprobe_xol_ops push_xol_ops = {
+	.emulate  = push_emulate_op,
+};
+
+/* Returns -ENOSYS if branch_xol_ops doesn't handle this insn */
+static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
+{
+	u8 opc1 = OPCODE1(insn);
+	insn_byte_t p;
+	int i;
+
+	switch (opc1) {
+	case 0xeb:	/* jmp 8 */
+	case 0xe9:	/* jmp 32 */
+	case 0x90:	/* prefix* + nop; same as jmp with .offs = 0 */
+		break;
+
+	case 0xe8:	/* call relative */
+		branch_clear_offset(auprobe, insn);
+		break;
+
+	case 0x0f:
+		if (insn->opcode.nbytes != 2)
+			return -ENOSYS;
+		/*
+		 * If it is a "near" conditional jmp, OPCODE2() - 0x10 matches
+		 * OPCODE1() of the "short" jmp which checks the same condition.
+		 */
+		opc1 = OPCODE2(insn) - 0x10;
+	default:
+		if (!is_cond_jmp_opcode(opc1))
+			return -ENOSYS;
+	}
+
+	/*
+	 * 16-bit overrides such as CALLW (66 e8 nn nn) are not supported.
+	 * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66 prefix.
+	 * No one uses these insns, reject any branch insns with such prefix.
+	 */
+	for_each_insn_prefix(insn, i, p) {
+		if (p == 0x66)
+			return -ENOTSUPP;
+	}
+
+	auprobe->branch.opc1 = opc1;
+	auprobe->branch.ilen = insn->length;
+	auprobe->branch.offs = insn->immediate.value;
+
+	auprobe->ops = &branch_xol_ops;
+	return 0;
+}
+
+/* Returns -ENOSYS if push_xol_ops doesn't handle this insn */
+static int push_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
+{
+	u8 opc1 = OPCODE1(insn), reg_offset = 0;
+
+	if (opc1 < 0x50 || opc1 > 0x57)
+		return -ENOSYS;
+
+	if (insn->length > 2)
+		return -ENOSYS;
+	if (insn->length == 2) {
+		/* only support rex_prefix 0x41 (x64 only) */
+#ifdef CONFIG_X86_64
+		if (insn->rex_prefix.nbytes != 1 ||
+		    insn->rex_prefix.bytes[0] != 0x41)
+			return -ENOSYS;
+
+		switch (opc1) {
+		case 0x50:
+			reg_offset = offsetof(struct pt_regs, r8);
+			break;
+		case 0x51:
+			reg_offset = offsetof(struct pt_regs, r9);
+			break;
+		case 0x52:
+			reg_offset = offsetof(struct pt_regs, r10);
+			break;
+		case 0x53:
+			reg_offset = offsetof(struct pt_regs, r11);
+			break;
+		case 0x54:
+			reg_offset = offsetof(struct pt_regs, r12);
+			break;
+		case 0x55:
+			reg_offset = offsetof(struct pt_regs, r13);
+			break;
+		case 0x56:
+			reg_offset = offsetof(struct pt_regs, r14);
+			break;
+		case 0x57:
+			reg_offset = offsetof(struct pt_regs, r15);
+			break;
+		}
+#else
+		return -ENOSYS;
+#endif
+	} else {
+		switch (opc1) {
+		case 0x50:
+			reg_offset = offsetof(struct pt_regs, ax);
+			break;
+		case 0x51:
+			reg_offset = offsetof(struct pt_regs, cx);
+			break;
+		case 0x52:
+			reg_offset = offsetof(struct pt_regs, dx);
+			break;
+		case 0x53:
+			reg_offset = offsetof(struct pt_regs, bx);
+			break;
+		case 0x54:
+			reg_offset = offsetof(struct pt_regs, sp);
+			break;
+		case 0x55:
+			reg_offset = offsetof(struct pt_regs, bp);
+			break;
+		case 0x56:
+			reg_offset = offsetof(struct pt_regs, si);
+			break;
+		case 0x57:
+			reg_offset = offsetof(struct pt_regs, di);
+			break;
+		}
+	}
+
+	auprobe->push.reg_offset = reg_offset;
+	auprobe->push.ilen = insn->length;
+	auprobe->ops = &push_xol_ops;
+	return 0;
+}
+
+/**
+ * arch_uprobe_analyze_insn - instruction analysis including validity and fixups.
+ * @mm: the probed address space.
+ * @arch_uprobe: the probepoint information.
+ * @addr: virtual address at which to install the probepoint
+ * Return 0 on success or a -ve number on error.
+ */
+int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long addr)
+{
+	struct insn insn;
+	u8 fix_ip_or_call = UPROBE_FIX_IP;
+	int ret;
+
+	ret = uprobe_init_insn(auprobe, &insn, is_64bit_mm(mm));
+	if (ret)
+		return ret;
+
+	ret = branch_setup_xol_ops(auprobe, &insn);
+	if (ret != -ENOSYS)
+		return ret;
+
+	ret = push_setup_xol_ops(auprobe, &insn);
+	if (ret != -ENOSYS)
+		return ret;
+
+	/*
+	 * Figure out which fixups default_post_xol_op() will need to perform,
+	 * and annotate defparam->fixups accordingly.
+	 */
+	switch (OPCODE1(&insn)) {
+	case 0x9d:		/* popf */
+		auprobe->defparam.fixups |= UPROBE_FIX_SETF;
+		break;
+	case 0xc3:		/* ret or lret -- ip is correct */
+	case 0xcb:
+	case 0xc2:
+	case 0xca:
+	case 0xea:		/* jmp absolute -- ip is correct */
+		fix_ip_or_call = 0;
+		break;
+	case 0x9a:		/* call absolute - Fix return addr, not ip */
+		fix_ip_or_call = UPROBE_FIX_CALL;
+		break;
+	case 0xff:
+		switch (MODRM_REG(&insn)) {
+		case 2: case 3:			/* call or lcall, indirect */
+			fix_ip_or_call = UPROBE_FIX_CALL;
+			break;
+		case 4: case 5:			/* jmp or ljmp, indirect */
+			fix_ip_or_call = 0;
+			break;
+		}
+		/* fall through */
+	default:
+		riprel_analyze(auprobe, &insn);
+	}
+
+	auprobe->defparam.ilen = insn.length;
+	auprobe->defparam.fixups |= fix_ip_or_call;
+
+	auprobe->ops = &default_xol_ops;
+	return 0;
+}
+
+/*
+ * arch_uprobe_pre_xol - prepare to execute out of line.
+ * @auprobe: the probepoint information.
+ * @regs: reflects the saved user state of current task.
+ */
+int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	if (auprobe->ops->pre_xol) {
+		int err = auprobe->ops->pre_xol(auprobe, regs);
+		if (err)
+			return err;
+	}
+
+	regs->ip = utask->xol_vaddr;
+	utask->autask.saved_trap_nr = current->thread.trap_nr;
+	current->thread.trap_nr = UPROBE_TRAP_NR;
+
+	utask->autask.saved_tf = !!(regs->flags & X86_EFLAGS_TF);
+	regs->flags |= X86_EFLAGS_TF;
+	if (test_tsk_thread_flag(current, TIF_BLOCKSTEP))
+		set_task_blockstep(current, false);
+
+	return 0;
+}
+
+/*
+ * If xol insn itself traps and generates a signal(Say,
+ * SIGILL/SIGSEGV/etc), then detect the case where a singlestepped
+ * instruction jumps back to its own address. It is assumed that anything
+ * like do_page_fault/do_trap/etc sets thread.trap_nr != -1.
+ *
+ * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
+ * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
+ * UPROBE_TRAP_NR == -1 set by arch_uprobe_pre_xol().
+ */
+bool arch_uprobe_xol_was_trapped(struct task_struct *t)
+{
+	if (t->thread.trap_nr != UPROBE_TRAP_NR)
+		return true;
+
+	return false;
+}
+
+/*
+ * Called after single-stepping. To avoid the SMP problems that can
+ * occur when we temporarily put back the original opcode to
+ * single-step, we single-stepped a copy of the instruction.
+ *
+ * This function prepares to resume execution after the single-step.
+ */
+int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+	bool send_sigtrap = utask->autask.saved_tf;
+	int err = 0;
+
+	WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
+	current->thread.trap_nr = utask->autask.saved_trap_nr;
+
+	if (auprobe->ops->post_xol) {
+		err = auprobe->ops->post_xol(auprobe, regs);
+		if (err) {
+			/*
+			 * Restore ->ip for restart or post mortem analysis.
+			 * ->post_xol() must not return -ERESTART unless this
+			 * is really possible.
+			 */
+			regs->ip = utask->vaddr;
+			if (err == -ERESTART)
+				err = 0;
+			send_sigtrap = false;
+		}
+	}
+	/*
+	 * arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP
+	 * so we can get an extra SIGTRAP if we do not clear TF. We need
+	 * to examine the opcode to make it right.
+	 */
+	if (send_sigtrap)
+		send_sig(SIGTRAP, current, 0);
+
+	if (!utask->autask.saved_tf)
+		regs->flags &= ~X86_EFLAGS_TF;
+
+	return err;
+}
+
+/* callback routine for handling exceptions. */
+int arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data)
+{
+	struct die_args *args = data;
+	struct pt_regs *regs = args->regs;
+	int ret = NOTIFY_DONE;
+
+	/* We are only interested in userspace traps */
+	if (regs && !user_mode(regs))
+		return NOTIFY_DONE;
+
+	switch (val) {
+	case DIE_INT3:
+		if (uprobe_pre_sstep_notifier(regs))
+			ret = NOTIFY_STOP;
+
+		break;
+
+	case DIE_DEBUG:
+		if (uprobe_post_sstep_notifier(regs))
+			ret = NOTIFY_STOP;
+
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+/*
+ * This function gets called when XOL instruction either gets trapped or
+ * the thread has a fatal signal. Reset the instruction pointer to its
+ * probed address for the potential restart or for post mortem analysis.
+ */
+void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	if (auprobe->ops->abort)
+		auprobe->ops->abort(auprobe, regs);
+
+	current->thread.trap_nr = utask->autask.saved_trap_nr;
+	regs->ip = utask->vaddr;
+	/* clear TF if it was set by us in arch_uprobe_pre_xol() */
+	if (!utask->autask.saved_tf)
+		regs->flags &= ~X86_EFLAGS_TF;
+}
+
+static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	if (auprobe->ops->emulate)
+		return auprobe->ops->emulate(auprobe, regs);
+	return false;
+}
+
+bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	bool ret = __skip_sstep(auprobe, regs);
+	if (ret && (regs->flags & X86_EFLAGS_TF))
+		send_sig(SIGTRAP, current, 0);
+	return ret;
+}
+
+unsigned long
+arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
+{
+	int rasize = sizeof_long(regs), nleft;
+	unsigned long orig_ret_vaddr = 0; /* clear high bits for 32-bit apps */
+
+	if (copy_from_user(&orig_ret_vaddr, (void __user *)regs->sp, rasize))
+		return -1;
+
+	/* check whether address has been already hijacked */
+	if (orig_ret_vaddr == trampoline_vaddr)
+		return orig_ret_vaddr;
+
+	nleft = copy_to_user((void __user *)regs->sp, &trampoline_vaddr, rasize);
+	if (likely(!nleft))
+		return orig_ret_vaddr;
+
+	if (nleft != rasize) {
+		pr_err("return address clobbered: pid=%d, %%sp=%#lx, %%ip=%#lx\n",
+		       current->pid, regs->sp, regs->ip);
+
+		force_sig(SIGSEGV, current);
+	}
+
+	return -1;
+}
+
+bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
+				struct pt_regs *regs)
+{
+	if (ctx == RP_CHECK_CALL) /* sp was just decremented by "call" insn */
+		return regs->sp < ret->stack;
+	else
+		return regs->sp <= ret->stack;
+}