From d139bca4b824ffb9731763c31b271a24b595948a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 22 Mar 2022 12:33:31 +0100 Subject: 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(-) (limited to 'tools') 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); } -- cgit v1.2.3 From 7a53f408902d913cd541b4f8ad7dbcd4961f5b82 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 23 Mar 2022 23:35:01 +0100 Subject: objtool: Fix SLS validation for kcov tail-call replacement Since not all compilers have a function attribute to disable KCOV instrumentation, objtool can rewrite KCOV instrumentation in noinstr functions as per commit: f56dae88a81f ("objtool: Handle __sanitize_cov*() tail calls") However, this has subtle interaction with the SLS validation from commit: 1cc1e4c8aab4 ("objtool: Add straight-line-speculation validation") In that when a tail-call instrucion is replaced with a RET an additional INT3 instruction is also written, but is not represented in the decoded instruction stream. This then leads to false positive missing INT3 objtool warnings in noinstr code. Instead of adding additional struct instruction objects, mark the RET instruction with retpoline_safe to suppress the warning (since we know there really is an INT3). Fixes: 1cc1e4c8aab4 ("objtool: Add straight-line-speculation validation") Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220323230712.GA8939@worktop.programming.kicks-ass.net --- tools/objtool/check.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'tools') diff --git a/tools/objtool/check.c b/tools/objtool/check.c index b848e1ddd5d8..bd0c2c828940 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1155,6 +1155,17 @@ static void annotate_call_site(struct objtool_file *file, : arch_nop_insn(insn->len)); insn->type = sibling ? INSN_RETURN : INSN_NOP; + + if (sibling) { + /* + * We've replaced the tail-call JMP insn by two new + * insn: RET; INT3, except we only have a single struct + * insn here. Mark it retpoline_safe to avoid the SLS + * warning, instead of adding another insn. + */ + insn->retpoline_safe = true; + } + return; } -- cgit v1.2.3