From: Pawan Gupta Date: Sat, 22 Jun 2024 04:17:21 +0000 (-0700) Subject: x86/its: Add support for ITS-safe return thunk X-Git-Tag: v6.1.139~10 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dbd8f170af4731d1251289a9419dae6f15a06308;p=thirdparty%2Fkernel%2Fstable.git x86/its: Add support for ITS-safe return thunk commit a75bf27fe41abe658c53276a0c486c4bf9adecfc upstream. RETs in the lower half of cacheline may be affected by ITS bug, specifically when the RSB-underflows. Use ITS-safe return thunk for such RETs. RETs that are not patched: - RET in retpoline sequence does not need to be patched, because the sequence itself fills an RSB before RET. - RET in Call Depth Tracking (CDT) thunks __x86_indirect_{call|jump}_thunk and call_depth_return_thunk are not patched because CDT by design prevents RSB-underflow. - RETs in .init section are not reachable after init. - RETs that are explicitly marked safe with ANNOTATE_UNRET_SAFE. Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Reviewed-by: Josh Poimboeuf Reviewed-by: Alexandre Chartre Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 9542c582d546b..2112939460856 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -81,6 +81,20 @@ extern void apply_ibt_endbr(s32 *start, s32 *end); struct module; +#if defined(CONFIG_RETHUNK) && defined(CONFIG_OBJTOOL) +extern bool cpu_wants_rethunk(void); +extern bool cpu_wants_rethunk_at(void *addr); +#else +static __always_inline bool cpu_wants_rethunk(void) +{ + return false; +} +static __always_inline bool cpu_wants_rethunk_at(void *addr) +{ + return false; +} +#endif + #ifdef CONFIG_SMP extern void alternatives_smp_module_add(struct module *mod, char *name, void *locks, void *locks_end, diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index b5ad7f5f73188..cccd5072e09f3 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -257,6 +257,12 @@ extern void __x86_return_thunk(void); static inline void __x86_return_thunk(void) {} #endif +#ifdef CONFIG_MITIGATION_ITS +extern void its_return_thunk(void); +#else +static inline void its_return_thunk(void) {} +#endif + extern void retbleed_return_thunk(void); extern void srso_return_thunk(void); extern void srso_alias_return_thunk(void); diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 0cb30cefb8edb..d70129eea9237 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -614,6 +614,21 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) #ifdef CONFIG_RETHUNK +bool cpu_wants_rethunk(void) +{ + return cpu_feature_enabled(X86_FEATURE_RETHUNK); +} + +bool cpu_wants_rethunk_at(void *addr) +{ + if (!cpu_feature_enabled(X86_FEATURE_RETHUNK)) + return false; + if (x86_return_thunk != its_return_thunk) + return true; + + return !((unsigned long)addr & 0x20); +} + /* * Rewrite the compiler generated return thunk tail-calls. * @@ -629,7 +644,7 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes) { int i = 0; - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { + if (cpu_wants_rethunk_at(addr)) { if (x86_return_thunk == __x86_return_thunk) return -1; diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index ec51ce713dea4..e737437015303 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -360,7 +360,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) goto fail; ip = trampoline + size; - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + if (cpu_wants_rethunk_at(ip)) __text_gen_insn(ip, JMP32_INSN_OPCODE, ip, x86_return_thunk, JMP32_INSN_SIZE); else memcpy(ip, retq, sizeof(retq)); diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index ca8dfc0c9edba..93809a4dc7936 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -79,7 +79,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, break; case RET: - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + if (cpu_wants_rethunk_at(insn)) code = text_gen_insn(JMP32_INSN_OPCODE, insn, x86_return_thunk); else code = &retinsn; diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 778ea89b737c4..35aeec9d22671 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -534,6 +534,10 @@ INIT_PER_CPU(irq_stack_backing_store); . = ASSERT(__x86_indirect_its_thunk_array == __x86_indirect_its_thunk_rax, "Gap in ITS thunk array"); #endif +#if defined(CONFIG_MITIGATION_ITS) && !defined(CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B) +. = ASSERT(its_return_thunk & 0x20, "its_return_thunk not in second half of cacheline"); +#endif + #endif /* CONFIG_X86_64 */ #ifdef CONFIG_KEXEC_CORE diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index be948f44fc241..e426615000948 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -284,7 +284,18 @@ SYM_CODE_START(__x86_indirect_its_thunk_array) .align 64, 0xcc SYM_CODE_END(__x86_indirect_its_thunk_array) -#endif +.align 64, 0xcc +.skip 32, 0xcc +SYM_CODE_START(its_return_thunk) + UNWIND_HINT_FUNC + ANNOTATE_NOENDBR + ANNOTATE_UNRET_SAFE + ret + int3 +SYM_CODE_END(its_return_thunk) +EXPORT_SYMBOL(its_return_thunk) + +#endif /* CONFIG_MITIGATION_ITS */ SYM_CODE_START(__x86_return_thunk) UNWIND_HINT_FUNC diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index c73d85255bbca..b5fd521a7fa05 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -487,7 +487,7 @@ static void emit_return(u8 **pprog, u8 *ip) { u8 *prog = *pprog; - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { + if (cpu_wants_rethunk()) { emit_jump(&prog, x86_return_thunk, ip); } else { EMIT1(0xC3); /* ret */