6.6-stable review patch. If anyone has any objections, please let me know.
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From: Pawan Gupta pawan.kumar.gupta@linux.intel.com
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 pawan.kumar.gupta@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Josh Poimboeuf jpoimboe@kernel.org Reviewed-by: Alexandre Chartre alexandre.chartre@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/alternative.h | 14 ++++++++++++++ arch/x86/include/asm/nospec-branch.h | 6 ++++++ arch/x86/kernel/alternative.c | 19 +++++++++++++++++-- arch/x86/kernel/ftrace.c | 2 +- arch/x86/kernel/static_call.c | 4 ++-- arch/x86/kernel/vmlinux.lds.S | 4 ++++ arch/x86/lib/retpoline.S | 13 ++++++++++++- arch/x86/net/bpf_jit_comp.c | 2 +- 8 files changed, 57 insertions(+), 7 deletions(-)
--- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -130,6 +130,20 @@ static __always_inline int x86_call_dept } #endif
+#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, --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -395,6 +395,12 @@ static inline void srso_return_thunk(voi static inline void srso_alias_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); --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -749,6 +749,21 @@ void __init_or_module noinline apply_ret
#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. * @@ -765,7 +780,7 @@ static int patch_return(void *addr, stru int i = 0;
/* Patch the custom return thunks... */ - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { + if (cpu_wants_rethunk_at(addr)) { i = JMP32_INSN_SIZE; __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i); } else { @@ -782,7 +797,7 @@ void __init_or_module noinline apply_ret { s32 *s;
- if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + if (cpu_wants_rethunk()) static_call_force_reinit();
for (s = start; s < end; s++) { --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -363,7 +363,7 @@ create_trampoline(struct ftrace_ops *ops 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)); --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -81,7 +81,7 @@ static void __ref __static_call_transfor 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; @@ -90,7 +90,7 @@ static void __ref __static_call_transfor case JCC: if (!func) { func = __static_call_return; - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + if (cpu_wants_rethunk()) func = x86_return_thunk; }
--- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -547,4 +547,8 @@ 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 */ --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -386,7 +386,18 @@ SYM_CODE_START(__x86_indirect_its_thunk_ .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 */
/* * This function name is magical and is used by -mfunction-return=thunk-extern --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -498,7 +498,7 @@ static void emit_return(u8 **pprog, u8 * { 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 */