Messages in this thread Patch in this message | | | Date | Tue, 2 Sep 2014 19:57:13 +0200 | From | Oleg Nesterov <> | Subject | [PATCH v2 1/7] x86, fpu: shift drop_init_fpu() from save_xstate_sig() to handle_signal() |
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save_xstate_sig()->drop_init_fpu() doesn't look right. setup_rt_frame() can fail after that, in this case the next setup_rt_frame() triggered by SIGSEGV won't save fpu simply because the old state was lost. This obviously mean that fpu won't be restored after sys_rt_sigreturn() from SIGSEGV handler.
Shift drop_init_fpu() into !failed branch in handle_signal().
Test-case (needs -O2):
#include <stdio.h> #include <signal.h> #include <unistd.h> #include <sys/syscall.h> #include <sys/mman.h> #include <pthread.h> #include <assert.h>
volatile double D;
void test(double d) { int pid = getpid();
for (D = d; D == d; ) { /* sys_tkill(pid, SIGHUP); asm to avoid save/reload * fp regs around "C" call */ asm ("" : : "a"(200), "D"(pid), "S"(1)); asm ("syscall" : : : "ax"); }
printf("ERR!!\n"); }
void sigh(int sig) { }
char altstack[4096 * 10] __attribute__((aligned(4096)));
void *tfunc(void *arg) { for (;;) { mprotect(altstack, sizeof(altstack), PROT_READ); mprotect(altstack, sizeof(altstack), PROT_READ|PROT_WRITE); } }
int main(void) { stack_t st = { .ss_sp = altstack, .ss_size = sizeof(altstack), .ss_flags = SS_ONSTACK, };
struct sigaction sa = { .sa_handler = sigh, };
pthread_t pt;
sigaction(SIGSEGV, &sa, NULL); sigaltstack(&st, NULL); sa.sa_flags = SA_ONSTACK; sigaction(SIGHUP, &sa, NULL);
pthread_create(&pt, NULL, tfunc, NULL);
test(123.456); return 0; }
Reported-by: Bean Anderson <bean@azulsystems.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: <stable@kernel.org> --- arch/x86/kernel/signal.c | 5 +++++ arch/x86/kernel/xsave.c | 2 -- 2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 2851d63..ed37a76 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -675,6 +675,11 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs) * handler too. */ regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF); + /* + * Ensure the signal handler starts with the new fpu state. + */ + if (used_math()) + drop_init_fpu(current); } signal_setup_done(failed, ksig, test_thread_flag(TIF_SINGLESTEP)); } diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c index a4b451c..74b34c2 100644 --- a/arch/x86/kernel/xsave.c +++ b/arch/x86/kernel/xsave.c @@ -268,8 +268,6 @@ int save_xstate_sig(void __user *buf, void __user *buf_fx, int size) if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate)) return -1; - drop_init_fpu(tsk); /* trigger finit */ - return 0; } -- 1.5.5.1
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