diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-09-14 14:52:37 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-09-20 13:38:33 +0300 |
| commit | 4586df06a02049f4315c25b947c6dde2627c0d18 (patch) | |
| tree | 67f5c953e8c470b70e033dcf2d5f8e1e9c66e9cf /arch | |
| parent | 33015556a943d6cbb18c555925a54b8c0e46f521 (diff) | |
| download | linux-4586df06a02049f4315c25b947c6dde2627c0d18.tar.xz | |
x86/ibt,ftrace: Make function-graph play nice
commit e52fc2cf3f662828cc0d51c4b73bed73ad275fce 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>
[OP: adjusted context for 5.10-stable]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/ftrace.c | 9 | ||||
| -rw-r--r-- | arch/x86/kernel/ftrace_64.S | 19 |
2 files changed, 17 insertions, 11 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 449e31a2f124..b80e38cbd49e 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -322,12 +322,12 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) 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; @@ -365,12 +365,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) 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) { diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S index e3a375185a1b..5b2dabedcf66 100644 --- a/arch/x86/kernel/ftrace_64.S +++ b/arch/x86/kernel/ftrace_64.S @@ -170,7 +170,6 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) /* * 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 @@ -325,7 +324,7 @@ SYM_FUNC_END(ftrace_graph_caller) SYM_CODE_START(return_to_handler) UNWIND_HINT_EMPTY - subq $24, %rsp + subq $16, %rsp /* Save the return values */ movq %rax, (%rsp) @@ -337,7 +336,19 @@ SYM_CODE_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_CODE_END(return_to_handler) #endif |