x86, fpu: shift drop_init_fpu() from save_xstate_sig() to handle_signal()
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>
Link: http://lkml.kernel.org/r/20140902175713.GA21646@redhat.com
Cc: <stable@kernel.org> # v3.7+
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
66463db4fc