| Date | Thu, 24 Feb 2022 15:51:52 +0100 | From | Peter Zijlstra <> | Subject | [PATCH v2 14/39] x86/ibt,ftrace: Make function-graph play nice |
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Return trampoline must not use indirect branch to return; while this preserves the RSB, it is fundamentally incompatible with IBT, reverts commit 194ec3418486 ("function-graph/x86: Replace unbalanced ret with jmp").
And since ftrace_stub no longer is 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> --- arch/x86/kernel/ftrace.c | 9 ++------- arch/x86/kernel/ftrace_64.S | 11 +++++++---- kernel/trace/ftrace.c | 10 ++++++++++ 3 files changed, 19 insertions(+), 11 deletions(-)
--- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -316,12 +316,12 @@ create_trampoline(struct ftrace_ops *ops unsigned long offset; unsigned long npages; unsigned long size; - unsigned long retq; unsigned long *ptr; void *trampoline; void *ip; /* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */ unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 }; + unsigned const char retq[] = { RET_INSN_OPCODE, INT3_INSN_OPCODE }; union ftrace_op_code_union op_ptr; int ret; @@ -359,12 +359,7 @@ create_trampoline(struct ftrace_ops *ops goto fail; ip = trampoline + size; - - /* The trampoline ends with ret(q) */ - retq = (unsigned long)ftrace_stub; - ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE); - if (WARN_ON(ret < 0)) - goto fail; + memcpy(ip, retq, RET_SIZE); /* No need to test direct calls on created trampolines */ if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { --- 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: @@ -316,10 +317,12 @@ SYM_FUNC_START(return_to_handler) call ftrace_return_to_handler - movq %rax, %rdi + movq %rax, 16(%rsp) movq 8(%rsp), %rdx movq (%rsp), %rax - addq $24, %rsp - JMP_NOSPEC rdi + + addq $16, %rsp + UNWIND_HINT_FUNC + RET SYM_FUNC_END(return_to_handler) #endif
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