Adding upstream version 6.1.76.upstream/6.1.76upstream

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

1 files changed, 270 insertions, 0 deletions

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
new file mode 100644
index 000000000..65c5c44f0
--- /dev/null
+++ b/arch/x86/lib/retpoline.S
@@ -0,0 +1,270 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/stringify.h>
+#include <linux/linkage.h>
+#include <asm/dwarf2.h>
+#include <asm/cpufeatures.h>
+#include <asm/alternative.h>
+#include <asm/export.h>
+#include <asm/nospec-branch.h>
+#include <asm/unwind_hints.h>
+#include <asm/frame.h>
+#include <asm/nops.h>
+
+	.section .text..__x86.indirect_thunk
+
+.macro RETPOLINE reg
+	ANNOTATE_INTRA_FUNCTION_CALL
+	call    .Ldo_rop_\@
+.Lspec_trap_\@:
+	UNWIND_HINT_EMPTY
+	pause
+	lfence
+	jmp .Lspec_trap_\@
+.Ldo_rop_\@:
+	mov     %\reg, (%_ASM_SP)
+	UNWIND_HINT_FUNC
+	RET
+.endm
+
+.macro THUNK reg
+
+	.align RETPOLINE_THUNK_SIZE
+SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
+	UNWIND_HINT_EMPTY
+	ANNOTATE_NOENDBR
+
+	ALTERNATIVE_2 __stringify(RETPOLINE \reg), \
+		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE, \
+		      __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), ALT_NOT(X86_FEATURE_RETPOLINE)
+
+.endm
+
+/*
+ * Despite being an assembler file we can't just use .irp here
+ * because __KSYM_DEPS__ only uses the C preprocessor and would
+ * only see one instance of "__x86_indirect_thunk_\reg" rather
+ * than one per register with the correct names. So we do it
+ * the simple and nasty way...
+ *
+ * Worse, you can only have a single EXPORT_SYMBOL per line,
+ * and CPP can't insert newlines, so we have to repeat everything
+ * at least twice.
+ */
+
+#define __EXPORT_THUNK(sym)	_ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym)
+#define EXPORT_THUNK(reg)	__EXPORT_THUNK(__x86_indirect_thunk_ ## reg)
+
+	.align RETPOLINE_THUNK_SIZE
+SYM_CODE_START(__x86_indirect_thunk_array)
+
+#define GEN(reg) THUNK reg
+#include <asm/GEN-for-each-reg.h>
+#undef GEN
+
+	.align RETPOLINE_THUNK_SIZE
+SYM_CODE_END(__x86_indirect_thunk_array)
+
+#define GEN(reg) EXPORT_THUNK(reg)
+#include <asm/GEN-for-each-reg.h>
+#undef GEN
+
+/*
+ * This function name is magical and is used by -mfunction-return=thunk-extern
+ * for the compiler to generate JMPs to it.
+ */
+#ifdef CONFIG_RETHUNK
+
+/*
+ * srso_alias_untrain_ret() and srso_alias_safe_ret() are placed at
+ * special addresses:
+ *
+ * - srso_alias_untrain_ret() is 2M aligned
+ * - srso_alias_safe_ret() is also in the same 2M page but bits 2, 8, 14
+ * and 20 in its virtual address are set (while those bits in the
+ * srso_alias_untrain_ret() function are cleared).
+ *
+ * This guarantees that those two addresses will alias in the branch
+ * target buffer of Zen3/4 generations, leading to any potential
+ * poisoned entries at that BTB slot to get evicted.
+ *
+ * As a result, srso_alias_safe_ret() becomes a safe return.
+ */
+#ifdef CONFIG_CPU_SRSO
+	.section .text..__x86.rethunk_untrain
+
+SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
+	UNWIND_HINT_FUNC
+	ANNOTATE_NOENDBR
+	ASM_NOP2
+	lfence
+	jmp srso_alias_return_thunk
+SYM_FUNC_END(srso_alias_untrain_ret)
+__EXPORT_THUNK(srso_alias_untrain_ret)
+
+	.section .text..__x86.rethunk_safe
+#else
+/* dummy definition for alternatives */
+SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
+SYM_FUNC_END(srso_alias_untrain_ret)
+#endif
+
+SYM_START(srso_alias_safe_ret, SYM_L_GLOBAL, SYM_A_NONE)
+	lea 8(%_ASM_SP), %_ASM_SP
+	UNWIND_HINT_FUNC
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
+SYM_FUNC_END(srso_alias_safe_ret)
+
+	.section .text..__x86.return_thunk
+
+SYM_CODE_START(srso_alias_return_thunk)
+	UNWIND_HINT_FUNC
+	ANNOTATE_NOENDBR
+	call srso_alias_safe_ret
+	ud2
+SYM_CODE_END(srso_alias_return_thunk)
+
+/*
+ * Some generic notes on the untraining sequences:
+ *
+ * They are interchangeable when it comes to flushing potentially wrong
+ * RET predictions from the BTB.
+ *
+ * The SRSO Zen1/2 (MOVABS) untraining sequence is longer than the
+ * Retbleed sequence because the return sequence done there
+ * (srso_safe_ret()) is longer and the return sequence must fully nest
+ * (end before) the untraining sequence. Therefore, the untraining
+ * sequence must fully overlap the return sequence.
+ *
+ * Regarding alignment - the instructions which need to be untrained,
+ * must all start at a cacheline boundary for Zen1/2 generations. That
+ * is, instruction sequences starting at srso_safe_ret() and
+ * the respective instruction sequences at retbleed_return_thunk()
+ * must start at a cacheline boundary.
+ */
+
+/*
+ * Safety details here pertain to the AMD Zen{1,2} microarchitecture:
+ * 1) The RET at retbleed_return_thunk must be on a 64 byte boundary, for
+ *    alignment within the BTB.
+ * 2) The instruction at retbleed_untrain_ret must contain, and not
+ *    end with, the 0xc3 byte of the RET.
+ * 3) STIBP must be enabled, or SMT disabled, to prevent the sibling thread
+ *    from re-poisioning the BTB prediction.
+ */
+	.align 64
+	.skip 64 - (retbleed_return_thunk - retbleed_untrain_ret), 0xcc
+SYM_START(retbleed_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
+	ANNOTATE_NOENDBR
+	/*
+	 * As executed from retbleed_untrain_ret, this is:
+	 *
+	 *   TEST $0xcc, %bl
+	 *   LFENCE
+	 *   JMP retbleed_return_thunk
+	 *
+	 * Executing the TEST instruction has a side effect of evicting any BTB
+	 * prediction (potentially attacker controlled) attached to the RET, as
+	 * retbleed_return_thunk + 1 isn't an instruction boundary at the moment.
+	 */
+	.byte	0xf6
+
+	/*
+	 * As executed from retbleed_return_thunk, this is a plain RET.
+	 *
+	 * As part of the TEST above, RET is the ModRM byte, and INT3 the imm8.
+	 *
+	 * We subsequently jump backwards and architecturally execute the RET.
+	 * This creates a correct BTB prediction (type=ret), but in the
+	 * meantime we suffer Straight Line Speculation (because the type was
+	 * no branch) which is halted by the INT3.
+	 *
+	 * With SMT enabled and STIBP active, a sibling thread cannot poison
+	 * RET's prediction to a type of its choice, but can evict the
+	 * prediction due to competitive sharing. If the prediction is
+	 * evicted, retbleed_return_thunk will suffer Straight Line Speculation
+	 * which will be contained safely by the INT3.
+	 */
+SYM_INNER_LABEL(retbleed_return_thunk, SYM_L_GLOBAL)
+	ret
+	int3
+SYM_CODE_END(retbleed_return_thunk)
+
+	/*
+	 * Ensure the TEST decoding / BTB invalidation is complete.
+	 */
+	lfence
+
+	/*
+	 * Jump back and execute the RET in the middle of the TEST instruction.
+	 * INT3 is for SLS protection.
+	 */
+	jmp retbleed_return_thunk
+	int3
+SYM_FUNC_END(retbleed_untrain_ret)
+__EXPORT_THUNK(retbleed_untrain_ret)
+
+/*
+ * SRSO untraining sequence for Zen1/2, similar to retbleed_untrain_ret()
+ * above. On kernel entry, srso_untrain_ret() is executed which is a
+ *
+ * movabs $0xccccc30824648d48,%rax
+ *
+ * and when the return thunk executes the inner label srso_safe_ret()
+ * later, it is a stack manipulation and a RET which is mispredicted and
+ * thus a "safe" one to use.
+ */
+	.align 64
+	.skip 64 - (srso_safe_ret - srso_untrain_ret), 0xcc
+SYM_START(srso_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
+	ANNOTATE_NOENDBR
+	.byte 0x48, 0xb8
+
+/*
+ * This forces the function return instruction to speculate into a trap
+ * (UD2 in srso_return_thunk() below).  This RET will then mispredict
+ * and execution will continue at the return site read from the top of
+ * the stack.
+ */
+SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL)
+	lea 8(%_ASM_SP), %_ASM_SP
+	ret
+	int3
+	int3
+	/* end of movabs */
+	lfence
+	call srso_safe_ret
+	ud2
+SYM_CODE_END(srso_safe_ret)
+SYM_FUNC_END(srso_untrain_ret)
+__EXPORT_THUNK(srso_untrain_ret)
+
+SYM_CODE_START(srso_return_thunk)
+	UNWIND_HINT_FUNC
+	ANNOTATE_NOENDBR
+	call srso_safe_ret
+	ud2
+SYM_CODE_END(srso_return_thunk)
+
+SYM_FUNC_START(entry_untrain_ret)
+	ALTERNATIVE_2 "jmp retbleed_untrain_ret", \
+		      "jmp srso_untrain_ret", X86_FEATURE_SRSO, \
+		      "jmp srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS
+SYM_FUNC_END(entry_untrain_ret)
+__EXPORT_THUNK(entry_untrain_ret)
+
+SYM_CODE_START(__x86_return_thunk)
+	UNWIND_HINT_FUNC
+	ANNOTATE_NOENDBR
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
+SYM_CODE_END(__x86_return_thunk)
+EXPORT_SYMBOL(__x86_return_thunk)
+
+#endif /* CONFIG_RETHUNK */