| /* 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/frame.h> |
| |
| #include <asm/alternative.h> |
| #include <asm/alternative-asm.h> |
| #include <asm/cpufeatures.h> |
| #include <asm/msr-index.h> |
| #include <asm/unwind_hints.h> |
| |
| /* |
| * 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 */ |
| |
| /* |
| * 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. |
| */ |
| #define __FILL_RETURN_BUFFER(reg, nr, sp) \ |
| mov $(nr/2), reg; \ |
| 771: \ |
| ANNOTATE_INTRA_FUNCTION_CALL; \ |
| call 772f; \ |
| 773: /* speculation trap */ \ |
| UNWIND_HINT_EMPTY; \ |
| pause; \ |
| lfence; \ |
| jmp 773b; \ |
| 772: \ |
| ANNOTATE_INTRA_FUNCTION_CALL; \ |
| call 774f; \ |
| 775: /* speculation trap */ \ |
| UNWIND_HINT_EMPTY; \ |
| pause; \ |
| lfence; \ |
| jmp 775b; \ |
| 774: \ |
| add $(BITS_PER_LONG/8) * 2, sp; \ |
| dec reg; \ |
| jnz 771b; |
| |
| #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 |
| |
| /* |
| * 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_retpoline_\reg), X86_FEATURE_RETPOLINE, \ |
| __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD |
| #else |
| jmp *%\reg |
| #endif |
| .endm |
| |
| .macro CALL_NOSPEC reg:req |
| #ifdef CONFIG_RETPOLINE |
| ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \ |
| __stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \ |
| __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD |
| #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 |
| #ifdef CONFIG_RETPOLINE |
| ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr |
| __FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP) |
| .Lskip_rsb_\@: |
| #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_RETPOLINE |
| #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_retpoline_%V[thunk_target]\n", \ |
| X86_FEATURE_RETPOLINE, \ |
| "lfence;\n" \ |
| ANNOTATE_RETPOLINE_SAFE \ |
| "call *%[thunk_target]\n", \ |
| X86_FEATURE_RETPOLINE_AMD) |
| |
| # 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_AMD) |
| |
| # 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_GENERIC, |
| SPECTRE_V2_RETPOLINE_AMD, |
| SPECTRE_V2_IBRS_ENHANCED, |
| }; |
| |
| /* 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"); |
| } |
| |
| static inline void indirect_branch_prediction_barrier(void) |
| { |
| u64 val = PRED_CMD_IBPB; |
| |
| alternative_msr_write(MSR_IA32_PRED_CMD, val, X86_FEATURE_USE_IBPB); |
| } |
| |
| /* The Intel SPEC CTRL MSR base value cache */ |
| extern u64 x86_spec_ctrl_base; |
| |
| /* |
| * 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 { \ |
| u64 val = x86_spec_ctrl_base | SPEC_CTRL_IBRS; \ |
| \ |
| preempt_disable(); \ |
| alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \ |
| X86_FEATURE_USE_IBRS_FW); \ |
| } while (0) |
| |
| #define firmware_restrict_branch_speculation_end() \ |
| do { \ |
| u64 val = x86_spec_ctrl_base; \ |
| \ |
| alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \ |
| 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); |
| |
| #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__ */ |
| |
| /* |
| * Below is used in the eBPF JIT compiler and emits the byte sequence |
| * for the following assembly: |
| * |
| * With retpolines configured: |
| * |
| * callq do_rop |
| * spec_trap: |
| * pause |
| * lfence |
| * jmp spec_trap |
| * do_rop: |
| * mov %rax,(%rsp) for x86_64 |
| * mov %edx,(%esp) for x86_32 |
| * retq |
| * |
| * Without retpolines configured: |
| * |
| * jmp *%rax for x86_64 |
| * jmp *%edx for x86_32 |
| */ |
| #ifdef CONFIG_RETPOLINE |
| # ifdef CONFIG_X86_64 |
| # define RETPOLINE_RAX_BPF_JIT_SIZE 17 |
| # define RETPOLINE_RAX_BPF_JIT() \ |
| do { \ |
| EMIT1_off32(0xE8, 7); /* callq do_rop */ \ |
| /* spec_trap: */ \ |
| EMIT2(0xF3, 0x90); /* pause */ \ |
| EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \ |
| EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \ |
| /* do_rop: */ \ |
| EMIT4(0x48, 0x89, 0x04, 0x24); /* mov %rax,(%rsp) */ \ |
| EMIT1(0xC3); /* retq */ \ |
| } while (0) |
| # else /* !CONFIG_X86_64 */ |
| # define RETPOLINE_EDX_BPF_JIT() \ |
| do { \ |
| EMIT1_off32(0xE8, 7); /* call do_rop */ \ |
| /* spec_trap: */ \ |
| EMIT2(0xF3, 0x90); /* pause */ \ |
| EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \ |
| EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \ |
| /* do_rop: */ \ |
| EMIT3(0x89, 0x14, 0x24); /* mov %edx,(%esp) */ \ |
| EMIT1(0xC3); /* ret */ \ |
| } while (0) |
| # endif |
| #else /* !CONFIG_RETPOLINE */ |
| # ifdef CONFIG_X86_64 |
| # define RETPOLINE_RAX_BPF_JIT_SIZE 2 |
| # define RETPOLINE_RAX_BPF_JIT() \ |
| EMIT2(0xFF, 0xE0); /* jmp *%rax */ |
| # else /* !CONFIG_X86_64 */ |
| # define RETPOLINE_EDX_BPF_JIT() \ |
| EMIT2(0xFF, 0xE2) /* jmp *%edx */ |
| # endif |
| #endif |
| |
| #endif /* _ASM_X86_NOSPEC_BRANCH_H_ */ |