6.6-stable review patch. If anyone has any objections, please let me know.
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From: Josh Poimboeuf jpoimboe@kernel.org
[ Upstream commit 8085fcd78c1a3dbdf2278732579009d41ce0bc4e ]
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 jpoimboe@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Brendan Jackman jackmanb@google.com Link: https://lore.kernel.org/r/d1f4026f8dc35d0de6cc61f2684e0cb6484009d1.174197534... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/traps.c | 18 +++++++++++++++++- tools/objtool/check.c | 31 +------------------------------ 2 files changed, 18 insertions(+), 31 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 37b8e20c03a9f..d8d9bc5a9b328 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -377,6 +377,21 @@ __visible void __noreturn handle_stack_overflow(struct pt_regs *regs, } #endif
+/* + * Prevent the compiler and/or objtool from marking the !CONFIG_X86_ESPFIX64 + * version of exc_double_fault() as noreturn. Otherwise the noreturn mismatch + * between configs triggers objtool warnings. + * + * This is a temporary hack until we have compiler or plugin support for + * annotating noreturns. + */ +#ifdef CONFIG_X86_ESPFIX64 +#define always_true() true +#else +bool always_true(void); +bool __weak always_true(void) { return true; } +#endif + /* * Runs on an IST stack for x86_64 and on a special task stack for x86_32. * @@ -512,7 +527,8 @@ DEFINE_IDTENTRY_DF(exc_double_fault)
pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code); die("double fault", regs, error_code); - panic("Machine halted."); + if (always_true()) + panic("Machine halted."); instrumentation_end(); }
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 6e59e7f578ffe..5824aa68ff961 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -4511,35 +4511,6 @@ 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; @@ -4556,7 +4527,7 @@ 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++;