linux-kernel - [PATCH] x86/signals: Fix save/restore signal stack to correctly support sigset

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Date:   Thu, 19 Nov 2020 14:11:33 -0800
From:   Walt Drummond <walt@...mmond.us>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, viro@...iv.linux.org.uk, brgerst@...il.com,
        linux@...inikbrodowski.net, walt@...mmond.us,
        gustavoars@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/signals: Fix save/restore signal stack to correctly support sigset_t

The macro unsafe_put_sigmask() only handles the first 64 bits of the
sigmask_t, which works today.  However, if the definition of the
sigset_t structure ever changed, this would fail to setup/restore the
signal stack properly and likely corrupt the sigset. This patch
updates unsafe_put_sigmask() to correctly save all the fields in the
sigmask_t struct, and adds unsafe_put_compat_sigmask() to handle the
compat_sigset_t cases.

Signed-off-by: Walt Drummond <walt@...mmond.us>
---
 arch/x86/kernel/signal.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index be0d7d4152ec..4d5134b4bb5f 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -203,11 +203,18 @@ do {									\
 		goto label;						\
 } while(0);
 
-#define unsafe_put_sigmask(set, frame, label) \
+#define unsafe_put_compat_sigmask(set, frame, label) \
 	unsafe_put_user(*(__u64 *)(set), \
 			(__u64 __user *)&(frame)->uc.uc_sigmask, \
 			label)
 
+#define unsafe_put_sigmask(set, frame, label)           \
+do {                                                    \
+	int i;								\
+	for (i = 0; i < _NSIG_WORDS; i++)				\
+		unsafe_put_user((set)->sig[i], &(frame)->uc.uc_sigmask.sig[i], label); \
+} while(0);
+
 /*
  * Set up a signal frame.
  */
@@ -566,7 +573,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
 	restorer = ksig->ka.sa.sa_restorer;
 	unsafe_put_user(restorer, (unsigned long __user *)&frame->pretcode, Efault);
 	unsafe_put_sigcontext(&frame->uc.uc_mcontext, fp, regs, set, Efault);
-	unsafe_put_sigmask(set, frame, Efault);
+	unsafe_put_compat_sigmask(set, frame, Efault);
 	user_access_end();
 
 	if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
@@ -643,7 +650,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
 	if (!access_ok(frame, sizeof(*frame)))
 		goto badframe;
-	if (__get_user(*(__u64 *)&set, (__u64 __user *)&frame->uc.uc_sigmask))
+	if (copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(sigset_t)))
 		goto badframe;
 	if (__get_user(uc_flags, &frame->uc.uc_flags))
 		goto badframe;
-- 
2.27.0