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authorPaul Mackerras <paulus@samba.org>2007-06-26 14:49:11 +1000
committerPaul Mackerras <paulus@samba.org>2007-06-26 14:49:11 +1000
commitae62fbb5f1f796d87cbdbe6701e13f2b52d5c0a7 (patch)
tree42c190d210c90876dbc799fd58896fbdce9164ce
parent74609f4536f2b8fd6a48381bbbe3cd37da20a527 (diff)
[POWERPC] Fix subtle FP state corruption bug in signal return on SMP
This fixes a bug which can cause corruption of the floating-point state on return from a signal handler. If we have a signal handler that has used the floating-point registers, and it happens to context-switch to another task while copying the interrupted floating-point state from the user stack into the thread struct (e.g. because of a page fault, or because it gets preempted), the context switch code will think that the FP registers contain valid FP state that needs to be copied into the thread_struct, and will thus overwrite the values that the signal return code has put into the thread_struct. This can occur because we clear the MSR bits that indicate the presence of valid FP state after copying the state into the thread_struct. To fix this we just move the clearing of the MSR bits to before the copy. A similar potential problem also occurs with the Altivec state, and this fixes that in the same way. Signed-off-by: Paul Mackerras <paulus@samba.org>
-rw-r--r--arch/powerpc/kernel/signal_64.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 1ce0ae3f6ff..b27e26852fd 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -176,6 +176,13 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
*/
discard_lazy_cpu_state();
+ /*
+ * Force reload of FP/VEC.
+ * This has to be done before copying stuff into current->thread.fpr/vr
+ * for the reasons explained in the previous comment.
+ */
+ regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC);
+
err |= __copy_from_user(&current->thread.fpr, &sc->fp_regs, FP_REGS_SIZE);
#ifdef CONFIG_ALTIVEC
@@ -197,9 +204,6 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
current->thread.vrsave = 0;
#endif /* CONFIG_ALTIVEC */
- /* Force reload of FP/VEC */
- regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC);
-
return err;
}