From: Paul Mackerras Date: Tue, 26 Jun 2007 04:49:11 +0000 (+1000) Subject: [POWERPC] Fix subtle FP state corruption bug in signal return on SMP X-Git-Tag: v2.6.22-rc7~48^2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ae62fbb5f1f796d87cbdbe6701e13f2b52d5c0a7;p=linux-2.6 [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 --- diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c index 1ce0ae3f6f..b27e26852f 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(¤t->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; }