Messages in this thread Patch in this message | | | Date | Mon, 2 May 2022 22:17:39 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] objtool: Fix SLS checks |
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On Mon, May 02, 2022 at 11:15:47AM -0700, Josh Poimboeuf wrote:
> From: Josh Poimboeuf <jpoimboe@redhat.com> > Subject: [PATCH] x86/speculation: Mitigate SLS for JMP_NOSPEC with retpolines disabled > > Having disabled retpolines doesn't necessarily mean the user doesn't > care about straight-line speculation. For example, retpolines are > disabled when eIBRS is used. > > If CONFIG_SLS is enabled, properly mitigate SLS for JMP_NOSPEC for the > retpolines disabled cases. > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > --- > arch/x86/include/asm/nospec-branch.h | 13 ++++++++++--- > tools/objtool/check.c | 3 --- > 2 files changed, 10 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > index acbaeaf83b61..0648746bf60b 100644 > --- a/arch/x86/include/asm/nospec-branch.h > +++ b/arch/x86/include/asm/nospec-branch.h > @@ -75,6 +75,13 @@ > .popsection > .endm > > +.macro INDIRECT_JMP reg > + jmp *%\reg > +#ifdef CONFIG_SLS > + int3 > +#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 > @@ -82,11 +89,11 @@ > */ > .macro JMP_NOSPEC reg:req > #ifdef CONFIG_RETPOLINE > - ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ > + ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), \ > __stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \ > - __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE > + __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), X86_FEATURE_RETPOLINE_LFENCE > #else > - jmp *%\reg > + INDIRECT_JMP \reg > #endif > .endm > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > index e7983c3e2408..3cf3ad0b5db5 100644 > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -3842,9 +3842,6 @@ static int validate_sls(struct objtool_file *file) > for_each_insn(file, insn) { > next_insn = next_insn_same_sec(file, insn); > > - if (insn->retpoline_safe) > - continue; > - > switch (insn->type) { > case INSN_RETURN: > if (!next_insn || next_insn->type != INSN_TRAP) {
Yes, agreed. But perhaps with something like this on top?
--- diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 3c66073e7645..84beeb5297d5 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -452,6 +452,17 @@ static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) return ret; i += ret; +#ifdef CONFIG_SLS + /* + * Ideally this would be unconditional, except in case of + * RETPOLINE_LFENCE we don't have sufficient space. Additionally, + * -mharden-sls=all should be extended to emit INT3 after + * direct jumps too, which will then cover that case. + */ + if (i < insn->length) + bytes[i++] = INT3_INSN_OPCODE; +#endif + for (; i < insn->length;) bytes[i++] = BYTES_NOP1; diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index b2b2366885a2..26e742da3129 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -33,9 +33,9 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) UNWIND_HINT_EMPTY ANNOTATE_NOENDBR - ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ + ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), \ __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \ - __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE + __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), X86_FEATURE_RETPOLINE_LFENCE .endm diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 16b6efacf7c6..6929856e7f6d 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -418,6 +418,10 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip) #endif EMIT2(0xFF, 0xE0 + reg); +#ifdef CONFIG_SLS + EMIT1(0xCC); +#endif + *pprog = prog; }
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