From d139bca4b824ffb9731763c31b271a24b595948a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 22 Mar 2022 12:33:31 +0100 Subject: [PATCH] objtool: Fix IBT tail-call detection Objtool reports: arch/x86/crypto/poly1305-x86_64.o: warning: objtool: poly1305_blocks_avx() falls through to next function poly1305_blocks_x86_64() arch/x86/crypto/poly1305-x86_64.o: warning: objtool: poly1305_emit_avx() falls through to next function poly1305_emit_x86_64() arch/x86/crypto/poly1305-x86_64.o: warning: objtool: poly1305_blocks_avx2() falls through to next function poly1305_blocks_x86_64() Which reads like: 0000000000000040 : 40: f3 0f 1e fa endbr64 ... 0000000000000400 : 400: f3 0f 1e fa endbr64 404: 44 8b 47 14 mov 0x14(%rdi),%r8d 408: 48 81 fa 80 00 00 00 cmp $0x80,%rdx 40f: 73 09 jae 41a 411: 45 85 c0 test %r8d,%r8d 414: 0f 84 2a fc ff ff je 44 ... These are simple conditional tail-calls and *should* be recognised as such by objtool, however due to a mistake in commit 08f87a93c8ec ("objtool: Validate IBT assumptions") this is failing. Specifically, the jump_dest is +4, this means the instruction pointed at will not be ENDBR and as such it will fail the second clause of is_first_func_insn() that was supposed to capture this exact case. Instead, have is_first_func_insn() look at the previous instruction. Fixes: 08f87a93c8ec ("objtool: Validate IBT assumptions") Reported-by: Stephen Rothwell Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220322115125.811582125@infradead.org --- tools/objtool/check.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 6de5085e3e5a..b848e1ddd5d8 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1239,11 +1239,20 @@ static bool same_function(struct instruction *insn1, struct instruction *insn2) return insn1->func->pfunc == insn2->func->pfunc; } -static bool is_first_func_insn(struct instruction *insn) +static bool is_first_func_insn(struct objtool_file *file, struct instruction *insn) { - return insn->offset == insn->func->offset || - (insn->type == INSN_ENDBR && - insn->offset == insn->func->offset + insn->len); + if (insn->offset == insn->func->offset) + return true; + + if (ibt) { + struct instruction *prev = prev_insn_same_sym(file, insn); + + if (prev && prev->type == INSN_ENDBR && + insn->offset == insn->func->offset + prev->len) + return true; + } + + return false; } /* @@ -1327,7 +1336,7 @@ static int add_jump_destinations(struct objtool_file *file) insn->jump_dest->func->pfunc = insn->func; } else if (!same_function(insn, insn->jump_dest) && - is_first_func_insn(insn->jump_dest)) { + is_first_func_insn(file, insn->jump_dest)) { /* internal sibling call (without reloc) */ add_call_dest(file, insn, insn->jump_dest->func, true); }