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| author | Peter Zijlstra <peterz@infradead.org> | 2022-03-08 16:30:31 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-03-15 10:32:37 +0100 |
| commit | e52fc2cf3f662828cc0d51c4b73bed73ad275fce (patch) | |
| tree | 66c13647656492fd38701ff5bf2adff25e6e4b20 /arch/x86/kernel/ftrace_64.S | |
| parent | d15cb3dab1e4f00e29599a4f5e1f6678a530d270 (diff) | |
| download | lwn-e52fc2cf3f662828cc0d51c4b73bed73ad275fce.tar.gz lwn-e52fc2cf3f662828cc0d51c4b73bed73ad275fce.zip | |
x86/ibt,ftrace: Make function-graph play nice
Return trampoline must not use indirect branch to return; while this
preserves the RSB, it is fundamentally incompatible with IBT. Instead
use a retpoline like ROP gadget that defeats IBT while not unbalancing
the RSB.
And since ftrace_stub is no longer a plain RET, don't use it to copy
from. Since RET is a trivial instruction, poke it directly.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.347296408@infradead.org
Diffstat (limited to 'arch/x86/kernel/ftrace_64.S')
| -rw-r--r-- | arch/x86/kernel/ftrace_64.S | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S index 11ac028e30e4..e32b5cd6dc15 100644 --- a/arch/x86/kernel/ftrace_64.S +++ b/arch/x86/kernel/ftrace_64.S @@ -176,10 +176,10 @@ SYM_FUNC_END(ftrace_caller); SYM_FUNC_START(ftrace_epilogue) /* * This is weak to keep gas from relaxing the jumps. - * It is also used to copy the RET for trampolines. */ SYM_INNER_LABEL_ALIGN(ftrace_stub, SYM_L_WEAK) UNWIND_HINT_FUNC + ENDBR RET SYM_FUNC_END(ftrace_epilogue) @@ -284,6 +284,7 @@ SYM_FUNC_START(__fentry__) jnz trace SYM_INNER_LABEL(ftrace_stub, SYM_L_GLOBAL) + ENDBR RET trace: @@ -307,7 +308,7 @@ EXPORT_SYMBOL(__fentry__) #ifdef CONFIG_FUNCTION_GRAPH_TRACER SYM_FUNC_START(return_to_handler) - subq $24, %rsp + subq $16, %rsp /* Save the return values */ movq %rax, (%rsp) @@ -319,7 +320,19 @@ SYM_FUNC_START(return_to_handler) movq %rax, %rdi movq 8(%rsp), %rdx movq (%rsp), %rax - addq $24, %rsp - JMP_NOSPEC rdi + + addq $16, %rsp + /* + * Jump back to the old return address. This cannot be JMP_NOSPEC rdi + * since IBT would demand that contain ENDBR, which simply isn't so for + * return addresses. Use a retpoline here to keep the RSB balanced. + */ + ANNOTATE_INTRA_FUNCTION_CALL + call .Ldo_rop + int3 +.Ldo_rop: + mov %rdi, (%rsp) + UNWIND_HINT_FUNC + RET SYM_FUNC_END(return_to_handler) #endif |