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x86/ibt,ftrace: Make function-graph play nice
commit e52fc2cf3f
upstream.
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
[cascardo: remove ENDBR]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
f663276348
commit
543138c555
2 changed files with 17 additions and 11 deletions
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@ -322,12 +322,12 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
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unsigned long offset;
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unsigned long npages;
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unsigned long size;
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unsigned long retq;
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unsigned long *ptr;
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void *trampoline;
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void *ip;
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/* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
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unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
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unsigned const char retq[] = { RET_INSN_OPCODE, INT3_INSN_OPCODE };
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union ftrace_op_code_union op_ptr;
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int ret;
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@ -365,12 +365,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
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goto fail;
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ip = trampoline + size;
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/* The trampoline ends with ret(q) */
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retq = (unsigned long)ftrace_stub;
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ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
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if (WARN_ON(ret < 0))
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goto fail;
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memcpy(ip, retq, RET_SIZE);
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/* No need to test direct calls on created trampolines */
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if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
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@ -181,7 +181,6 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL)
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/*
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* This is weak to keep gas from relaxing the jumps.
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* It is also used to copy the RET for trampolines.
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*/
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SYM_INNER_LABEL_ALIGN(ftrace_stub, SYM_L_WEAK)
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UNWIND_HINT_FUNC
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@ -335,7 +334,7 @@ SYM_FUNC_START(ftrace_graph_caller)
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SYM_FUNC_END(ftrace_graph_caller)
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SYM_FUNC_START(return_to_handler)
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subq $24, %rsp
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subq $16, %rsp
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/* Save the return values */
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movq %rax, (%rsp)
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@ -347,7 +346,19 @@ SYM_FUNC_START(return_to_handler)
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movq %rax, %rdi
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movq 8(%rsp), %rdx
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movq (%rsp), %rax
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addq $24, %rsp
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JMP_NOSPEC rdi
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addq $16, %rsp
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/*
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* Jump back to the old return address. This cannot be JMP_NOSPEC rdi
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* since IBT would demand that contain ENDBR, which simply isn't so for
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* return addresses. Use a retpoline here to keep the RSB balanced.
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*/
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ANNOTATE_INTRA_FUNCTION_CALL
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call .Ldo_rop
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int3
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.Ldo_rop:
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mov %rdi, (%rsp)
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UNWIND_HINT_FUNC
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RET
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SYM_FUNC_END(return_to_handler)
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#endif
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