From 8085fcd78c1a3dbdf2278732579009d41ce0bc4e Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Fri, 14 Mar 2025 12:28:59 -0700 Subject: x86/traps: Make exc_double_fault() consistently noreturn The CONFIG_X86_ESPFIX64 version of exc_double_fault() can return to its caller, but the !CONFIG_X86_ESPFIX64 version never does. In the latter case the compiler and/or objtool may consider it to be implicitly noreturn. However, due to the currently inflexible way objtool detects noreturns, a function's noreturn status needs to be consistent across configs. The current workaround for this issue is to suppress unreachable warnings for exc_double_fault()'s callers. Unfortunately that can result in ORC coverage gaps and potentially worse issues like inert static calls and silently disabled CPU mitigations. Instead, prevent exc_double_fault() from ever being implicitly marked noreturn by forcing a return behind a never-taken conditional. Until a more integrated noreturn detection method exists, this is likely the least objectionable workaround. Fixes: 55eeab2a8a11 ("objtool: Ignore exc_double_fault() __noreturn warnings") Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Brendan Jackman Link: https://lore.kernel.org/r/d1f4026f8dc35d0de6cc61f2684e0cb6484009d1.1741975349.git.jpoimboe@kernel.org --- tools/objtool/check.c | 31 +------------------------------ 1 file changed, 1 insertion(+), 30 deletions(-) (limited to 'tools/objtool') diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 7dbf22c6da9d..12bf6c1f5071 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -4460,35 +4460,6 @@ static int validate_sls(struct objtool_file *file) return warnings; } -static bool ignore_noreturn_call(struct instruction *insn) -{ - struct symbol *call_dest = insn_call_dest(insn); - - /* - * FIXME: hack, we need a real noreturn solution - * - * Problem is, exc_double_fault() may or may not return, depending on - * whether CONFIG_X86_ESPFIX64 is set. But objtool has no visibility - * to the kernel config. - * - * Other potential ways to fix it: - * - * - have compiler communicate __noreturn functions somehow - * - remove CONFIG_X86_ESPFIX64 - * - read the .config file - * - add a cmdline option - * - create a generic objtool annotation format (vs a bunch of custom - * formats) and annotate it - */ - if (!strcmp(call_dest->name, "exc_double_fault")) { - /* prevent further unreachable warnings for the caller */ - insn->sym->warned = 1; - return true; - } - - return false; -} - static int validate_reachable_instructions(struct objtool_file *file) { struct instruction *insn, *prev_insn; @@ -4505,7 +4476,7 @@ static int validate_reachable_instructions(struct objtool_file *file) prev_insn = prev_insn_same_sec(file, insn); if (prev_insn && prev_insn->dead_end) { call_dest = insn_call_dest(prev_insn); - if (call_dest && !ignore_noreturn_call(prev_insn)) { + if (call_dest) { WARN_INSN(insn, "%s() is missing a __noreturn annotation", call_dest->name); warnings++; -- cgit v1.2.3