diff options
Diffstat (limited to 'arch/x86/include/asm/nospec-branch.h')
| -rw-r--r-- | arch/x86/include/asm/nospec-branch.h | 412 |
1 files changed, 412 insertions, 0 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h new file mode 100644 index 000000000..7b4782249 --- /dev/null +++ b/arch/x86/include/asm/nospec-branch.h @@ -0,0 +1,412 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _ASM_X86_NOSPEC_BRANCH_H_ +#define _ASM_X86_NOSPEC_BRANCH_H_ + +#include <linux/static_key.h> +#include <linux/objtool.h> +#include <linux/linkage.h> + +#include <asm/alternative.h> +#include <asm/cpufeatures.h> +#include <asm/msr-index.h> +#include <asm/unwind_hints.h> +#include <asm/percpu.h> + +#define RETPOLINE_THUNK_SIZE 32 + +/* + * Fill the CPU return stack buffer. + * + * Each entry in the RSB, if used for a speculative 'ret', contains an + * infinite 'pause; lfence; jmp' loop to capture speculative execution. + * + * This is required in various cases for retpoline and IBRS-based + * mitigations for the Spectre variant 2 vulnerability. Sometimes to + * eliminate potentially bogus entries from the RSB, and sometimes + * purely to ensure that it doesn't get empty, which on some CPUs would + * allow predictions from other (unwanted!) sources to be used. + * + * We define a CPP macro such that it can be used from both .S files and + * inline assembly. It's possible to do a .macro and then include that + * from C via asm(".include <asm/nospec-branch.h>") but let's not go there. + */ + +#define RSB_CLEAR_LOOPS 32 /* To forcibly overwrite all entries */ + +/* + * Common helper for __FILL_RETURN_BUFFER and __FILL_ONE_RETURN. + */ +#define __FILL_RETURN_SLOT \ + ANNOTATE_INTRA_FUNCTION_CALL; \ + call 772f; \ + int3; \ +772: + +/* + * Stuff the entire RSB. + * + * Google experimented with loop-unrolling and this turned out to be + * the optimal version — two calls, each with their own speculation + * trap should their return address end up getting used, in a loop. + */ +#ifdef CONFIG_X86_64 +#define __FILL_RETURN_BUFFER(reg, nr) \ + mov $(nr/2), reg; \ +771: \ + __FILL_RETURN_SLOT \ + __FILL_RETURN_SLOT \ + add $(BITS_PER_LONG/8) * 2, %_ASM_SP; \ + dec reg; \ + jnz 771b; \ + /* barrier for jnz misprediction */ \ + lfence; +#else +/* + * i386 doesn't unconditionally have LFENCE, as such it can't + * do a loop. + */ +#define __FILL_RETURN_BUFFER(reg, nr) \ + .rept nr; \ + __FILL_RETURN_SLOT; \ + .endr; \ + add $(BITS_PER_LONG/8) * nr, %_ASM_SP; +#endif + +/* + * Stuff a single RSB slot. + * + * To mitigate Post-Barrier RSB speculation, one CALL instruction must be + * forced to retire before letting a RET instruction execute. + * + * On PBRSB-vulnerable CPUs, it is not safe for a RET to be executed + * before this point. + */ +#define __FILL_ONE_RETURN \ + __FILL_RETURN_SLOT \ + add $(BITS_PER_LONG/8), %_ASM_SP; \ + lfence; + +#ifdef __ASSEMBLY__ + +/* + * This should be used immediately before an indirect jump/call. It tells + * objtool the subsequent indirect jump/call is vouched safe for retpoline + * builds. + */ +.macro ANNOTATE_RETPOLINE_SAFE + .Lannotate_\@: + .pushsection .discard.retpoline_safe + _ASM_PTR .Lannotate_\@ + .popsection +.endm + +/* + * (ab)use RETPOLINE_SAFE on RET to annotate away 'bare' RET instructions + * vs RETBleed validation. + */ +#define ANNOTATE_UNRET_SAFE ANNOTATE_RETPOLINE_SAFE + +/* + * Abuse ANNOTATE_RETPOLINE_SAFE on a NOP to indicate UNRET_END, should + * eventually turn into it's own annotation. + */ +.macro ANNOTATE_UNRET_END +#if (defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_SRSO)) + ANNOTATE_RETPOLINE_SAFE + nop +#endif +.endm + +/* + * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple + * indirect jmp/call which may be susceptible to the Spectre variant 2 + * attack. + */ +.macro JMP_NOSPEC reg:req +#ifdef CONFIG_RETPOLINE + ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ + __stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \ + __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE +#else + jmp *%\reg +#endif +.endm + +.macro CALL_NOSPEC reg:req +#ifdef CONFIG_RETPOLINE + ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \ + __stringify(call __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \ + __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_LFENCE +#else + call *%\reg +#endif +.endm + + /* + * A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP + * monstrosity above, manually. + */ +.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req ftr2=ALT_NOT(X86_FEATURE_ALWAYS) + ALTERNATIVE_2 "jmp .Lskip_rsb_\@", \ + __stringify(__FILL_RETURN_BUFFER(\reg,\nr)), \ftr, \ + __stringify(__FILL_ONE_RETURN), \ftr2 + +.Lskip_rsb_\@: +.endm + +#ifdef CONFIG_CPU_UNRET_ENTRY +#define CALL_UNTRAIN_RET "call entry_untrain_ret" +#else +#define CALL_UNTRAIN_RET "" +#endif + +/* + * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the + * return thunk isn't mapped into the userspace tables (then again, AMD + * typically has NO_MELTDOWN). + * + * While retbleed_untrain_ret() doesn't clobber anything but requires stack, + * entry_ibpb() will clobber AX, CX, DX. + * + * As such, this must be placed after every *SWITCH_TO_KERNEL_CR3 at a point + * where we have a stack but before any RET instruction. + */ +.macro UNTRAIN_RET +#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) || \ + defined(CONFIG_CPU_SRSO) + ANNOTATE_UNRET_END + ALTERNATIVE_2 "", \ + CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \ + "call entry_ibpb", X86_FEATURE_ENTRY_IBPB +#endif +.endm + +#else /* __ASSEMBLY__ */ + +#define ANNOTATE_RETPOLINE_SAFE \ + "999:\n\t" \ + ".pushsection .discard.retpoline_safe\n\t" \ + _ASM_PTR " 999b\n\t" \ + ".popsection\n\t" + +#ifdef CONFIG_RETHUNK +extern void __x86_return_thunk(void); +#else +static inline void __x86_return_thunk(void) {} +#endif + +extern void retbleed_return_thunk(void); +extern void srso_return_thunk(void); +extern void srso_alias_return_thunk(void); + +extern void retbleed_untrain_ret(void); +extern void srso_untrain_ret(void); +extern void srso_alias_untrain_ret(void); + +extern void entry_untrain_ret(void); +extern void entry_ibpb(void); + +#ifdef CONFIG_RETPOLINE + +typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE]; + +#define GEN(reg) \ + extern retpoline_thunk_t __x86_indirect_thunk_ ## reg; +#include <asm/GEN-for-each-reg.h> +#undef GEN + +extern retpoline_thunk_t __x86_indirect_thunk_array[]; + +#ifdef CONFIG_X86_64 + +/* + * Inline asm uses the %V modifier which is only in newer GCC + * which is ensured when CONFIG_RETPOLINE is defined. + */ +# define CALL_NOSPEC \ + ALTERNATIVE_2( \ + ANNOTATE_RETPOLINE_SAFE \ + "call *%[thunk_target]\n", \ + "call __x86_indirect_thunk_%V[thunk_target]\n", \ + X86_FEATURE_RETPOLINE, \ + "lfence;\n" \ + ANNOTATE_RETPOLINE_SAFE \ + "call *%[thunk_target]\n", \ + X86_FEATURE_RETPOLINE_LFENCE) + +# define THUNK_TARGET(addr) [thunk_target] "r" (addr) + +#else /* CONFIG_X86_32 */ +/* + * For i386 we use the original ret-equivalent retpoline, because + * otherwise we'll run out of registers. We don't care about CET + * here, anyway. + */ +# define CALL_NOSPEC \ + ALTERNATIVE_2( \ + ANNOTATE_RETPOLINE_SAFE \ + "call *%[thunk_target]\n", \ + " jmp 904f;\n" \ + " .align 16\n" \ + "901: call 903f;\n" \ + "902: pause;\n" \ + " lfence;\n" \ + " jmp 902b;\n" \ + " .align 16\n" \ + "903: lea 4(%%esp), %%esp;\n" \ + " pushl %[thunk_target];\n" \ + " ret;\n" \ + " .align 16\n" \ + "904: call 901b;\n", \ + X86_FEATURE_RETPOLINE, \ + "lfence;\n" \ + ANNOTATE_RETPOLINE_SAFE \ + "call *%[thunk_target]\n", \ + X86_FEATURE_RETPOLINE_LFENCE) + +# define THUNK_TARGET(addr) [thunk_target] "rm" (addr) +#endif +#else /* No retpoline for C / inline asm */ +# define CALL_NOSPEC "call *%[thunk_target]\n" +# define THUNK_TARGET(addr) [thunk_target] "rm" (addr) +#endif + +/* The Spectre V2 mitigation variants */ +enum spectre_v2_mitigation { + SPECTRE_V2_NONE, + SPECTRE_V2_RETPOLINE, + SPECTRE_V2_LFENCE, + SPECTRE_V2_EIBRS, + SPECTRE_V2_EIBRS_RETPOLINE, + SPECTRE_V2_EIBRS_LFENCE, + SPECTRE_V2_IBRS, +}; + +/* The indirect branch speculation control variants */ +enum spectre_v2_user_mitigation { + SPECTRE_V2_USER_NONE, + SPECTRE_V2_USER_STRICT, + SPECTRE_V2_USER_STRICT_PREFERRED, + SPECTRE_V2_USER_PRCTL, + SPECTRE_V2_USER_SECCOMP, +}; + +/* The Speculative Store Bypass disable variants */ +enum ssb_mitigation { + SPEC_STORE_BYPASS_NONE, + SPEC_STORE_BYPASS_DISABLE, + SPEC_STORE_BYPASS_PRCTL, + SPEC_STORE_BYPASS_SECCOMP, +}; + +extern char __indirect_thunk_start[]; +extern char __indirect_thunk_end[]; + +static __always_inline +void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature) +{ + asm volatile(ALTERNATIVE("", "wrmsr", %c[feature]) + : : "c" (msr), + "a" ((u32)val), + "d" ((u32)(val >> 32)), + [feature] "i" (feature) + : "memory"); +} + +extern u64 x86_pred_cmd; + +static inline void indirect_branch_prediction_barrier(void) +{ + alternative_msr_write(MSR_IA32_PRED_CMD, x86_pred_cmd, X86_FEATURE_USE_IBPB); +} + +/* The Intel SPEC CTRL MSR base value cache */ +extern u64 x86_spec_ctrl_base; +DECLARE_PER_CPU(u64, x86_spec_ctrl_current); +extern void update_spec_ctrl_cond(u64 val); +extern u64 spec_ctrl_current(void); + +/* + * With retpoline, we must use IBRS to restrict branch prediction + * before calling into firmware. + * + * (Implemented as CPP macros due to header hell.) + */ +#define firmware_restrict_branch_speculation_start() \ +do { \ + preempt_disable(); \ + alternative_msr_write(MSR_IA32_SPEC_CTRL, \ + spec_ctrl_current() | SPEC_CTRL_IBRS, \ + X86_FEATURE_USE_IBRS_FW); \ + alternative_msr_write(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, \ + X86_FEATURE_USE_IBPB_FW); \ +} while (0) + +#define firmware_restrict_branch_speculation_end() \ +do { \ + alternative_msr_write(MSR_IA32_SPEC_CTRL, \ + spec_ctrl_current(), \ + X86_FEATURE_USE_IBRS_FW); \ + preempt_enable(); \ +} while (0) + +DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); +DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); +DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); + +DECLARE_STATIC_KEY_FALSE(mds_user_clear); +DECLARE_STATIC_KEY_FALSE(mds_idle_clear); + +DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear); + +#include <asm/segment.h> + +/** + * mds_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability + * + * This uses the otherwise unused and obsolete VERW instruction in + * combination with microcode which triggers a CPU buffer flush when the + * instruction is executed. + */ +static __always_inline void mds_clear_cpu_buffers(void) +{ + static const u16 ds = __KERNEL_DS; + + /* + * Has to be the memory-operand variant because only that + * guarantees the CPU buffer flush functionality according to + * documentation. The register-operand variant does not. + * Works with any segment selector, but a valid writable + * data segment is the fastest variant. + * + * "cc" clobber is required because VERW modifies ZF. + */ + asm volatile("verw %[ds]" : : [ds] "m" (ds) : "cc"); +} + +/** + * mds_user_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability + * + * Clear CPU buffers if the corresponding static key is enabled + */ +static __always_inline void mds_user_clear_cpu_buffers(void) +{ + if (static_branch_likely(&mds_user_clear)) + mds_clear_cpu_buffers(); +} + +/** + * mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * Clear CPU buffers if the corresponding static key is enabled + */ +static inline void mds_idle_clear_cpu_buffers(void) +{ + if (static_branch_likely(&mds_idle_clear)) + mds_clear_cpu_buffers(); +} + +#endif /* __ASSEMBLY__ */ + +#endif /* _ASM_X86_NOSPEC_BRANCH_H_ */ |