From 02bed6bd5f45819f1557a4b04db300a72383ecdb Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Mon, 20 Mar 2017 11:31:44 +0000 Subject: [PATCH] user-exec: handle synchronous signals from QEMU gracefully MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When "tcg: enable thread-per-vCPU" (commit 3725794) was merged the lifetime of current_cpu was changed. Previously a broken linux-user call might abort() which can eventually escalate into a SIGSEGV which would then crash qemu as it attempted to deref a NULL current_cpu. After commit 3725794 it would attempt to fixup state and re-start the run-loop and much hilarity (i.e. a looping lockup) would ensue from jumping into a stale jmp_env. As we can actually tell if we are in the run-loop from looking at the cpu->running flag we should catch this badness first and abort() cleanly rather than try to soldier on. There is a theoretical race between the flag being set and sigsetjmp refreshing the jump buffer but we can try really hard to not introduce crashes into that code. [LV: setgroups03 fails on powerpc LTP] Reported-by: Laurent Vivier Signed-off-by: Alex Bennée Reviewed-by: Richard Henderson Reviewed-by: Paolo Bonzini --- user-exec.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/user-exec.c b/user-exec.c index 6db075884d..a8f95fa1e1 100644 --- a/user-exec.c +++ b/user-exec.c @@ -57,10 +57,23 @@ static void cpu_exit_tb_from_sighandler(CPUState *cpu, sigset_t *old_set) static inline int handle_cpu_signal(uintptr_t pc, unsigned long address, int is_write, sigset_t *old_set) { - CPUState *cpu; + CPUState *cpu = current_cpu; CPUClass *cc; int ret; + /* For synchronous signals we expect to be coming from the vCPU + * thread (so current_cpu should be valid) and either from running + * code or during translation which can fault as we cross pages. + * + * If neither is true then something has gone wrong and we should + * abort rather than try and restart the vCPU execution. + */ + if (!cpu || !cpu->running) { + printf("qemu:%s received signal outside vCPU context @ pc=0x%" + PRIxPTR "\n", __func__, pc); + abort(); + } + #if defined(DEBUG_SIGNAL) printf("qemu: SIGSEGV pc=0x%08lx address=%08lx w=%d oldset=0x%08lx\n", pc, address, is_write, *(unsigned long *)old_set); @@ -83,7 +96,7 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned long address, * currently executing TB was modified and must be exited * immediately. */ - cpu_exit_tb_from_sighandler(current_cpu, old_set); + cpu_exit_tb_from_sighandler(cpu, old_set); g_assert_not_reached(); default: g_assert_not_reached(); @@ -94,7 +107,6 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned long address, are still valid segv ones */ address = h2g_nocheck(address); - cpu = current_cpu; cc = CPU_GET_CLASS(cpu); /* see if it is an MMU fault */ g_assert(cc->handle_mmu_fault);