@@ -1462,10 +1462,33 @@ static int setup_return(struct pt_regs *regs, struct ksignal *ksig,
struct rt_sigframe_user_layout *user, int usig)
{
__sigrestore_t sigtramp;
+ int err;
+
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
+ sigtramp = ksig->ka.sa.sa_restorer;
+ else
+ sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp);
+
+ err = gcs_signal_entry(sigtramp, ksig);
+ if (err)
+ return err;
+
+ /*
+ * We must not fail from this point onwards. We are going to update
+ * registers, including SP, in order to invoke the signal handler. If
+ * we failed and attempted to deliver a nested SIGSEGV to a handler
+ * after that point, the subsequent sigreturn would end up restoring
+ * the (partial) state for the original signal handler.
+ */
regs->regs[0] = usig;
+ if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
+ regs->regs[1] = (unsigned long)&user->sigframe->info;
+ regs->regs[2] = (unsigned long)&user->sigframe->uc;
+ }
regs->sp = (unsigned long)user->sigframe;
regs->regs[29] = (unsigned long)&user->next_frame->fp;
+ regs->regs[30] = (unsigned long)sigtramp;
regs->pc = (unsigned long)ksig->ka.sa.sa_handler;
/*
@@ -1506,14 +1529,7 @@ static int setup_return(struct pt_regs *regs, struct ksignal *ksig,
sme_smstop();
}
- if (ksig->ka.sa.sa_flags & SA_RESTORER)
- sigtramp = ksig->ka.sa.sa_restorer;
- else
- sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp);
-
- regs->regs[30] = (unsigned long)sigtramp;
-
- return gcs_signal_entry(sigtramp, ksig);
+ return 0;
}
static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
@@ -1537,14 +1553,16 @@ static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
err |= setup_sigframe(&user, regs, set, &ua_state);
- if (err == 0) {
+ if (ksig->ka.sa.sa_flags & SA_SIGINFO)
+ err |= copy_siginfo_to_user(&frame->info, &ksig->info);
+
+ if (err == 0)
err = setup_return(regs, ksig, &user, usig);
- if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
- err |= copy_siginfo_to_user(&frame->info, &ksig->info);
- regs->regs[1] = (unsigned long)&frame->info;
- regs->regs[2] = (unsigned long)&frame->uc;
- }
- }
+
+ /*
+ * We must not fail if setup_return() succeeded - see comment at the
+ * beginning of setup_return().
+ */
if (err == 0)
set_handler_user_access_state();
Commit eaf62ce1563b ("arm64/signal: Set up and restore the GCS context for signal handlers") introduced a potential failure point at the end of setup_return(). This is unfortunate as it is too late to deliver a SIGSEGV: if that SIGSEGV is handled, the subsequent sigreturn will end up returning to the original handler, which is not the intention (since we failed to deliver that signal). Make sure this does not happen by calling gcs_signal_entry() at the very beginning of setup_return(), and add a comment just after to discourage error cases being introduced from that point onwards. While at it, also take care of copy_siginfo_to_user(): since it may fail, we shouldn't be calling it after setup_return() either. Call it before setup_return() instead, and move the setting of X1/X2 inside setup_return() where it belongs (after the "point of no failure"). Background: the first part of setup_rt_frame(), including setup_sigframe(), has no impact on the execution of the interrupted thread. The signal frame is written to the stack, but the stack pointer remains unchanged. Failure at this stage can be recovered by a SIGSEGV handler, and sigreturn will restore the original context, at the point where the original signal occurred. On the other hand, once setup_return() has updated registers including SP, the thread's control flow has been modified and we must deliver the original signal. Fixes: eaf62ce1563b ("arm64/signal: Set up and restore the GCS context for signal handlers") Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com> --- v1..v2: * Added a short comment in setup_rt_frame() after the call to setup_return() to discourage adding failure points there. [Dave's suggestion] Cc: broonie@kernel.org Cc: catalin.marinas@arm.com Cc: Dave.Martin@arm.com Cc: will@kernel.org --- arch/arm64/kernel/signal.c | 48 ++++++++++++++++++++++++++------------ 1 file changed, 33 insertions(+), 15 deletions(-) base-commit: fac04efc5c793dccbd07e2d59af9f90b7fc0dca4