[PATCH AUTOSEL 6.10 086/197] x86/pkeys: Restore altstack access in sigreturn()

[Sasha Levin]

From: Aruna Ramakrishna <aruna.ramakrishna@xxxxxxxxxx>

[ Upstream commit d10b554919d4cc8fa8fe2e95b57ad2624728c8e4 ]

A process can disable access to the alternate signal stack by not
enabling the altstack's PKEY in the PKRU register.

Nevertheless, the kernel updates the PKRU temporarily for signal
handling. However, in sigreturn(), restore_sigcontext() will restore the
PKRU to the user-defined PKRU value.

This will cause restore_altstack() to fail with a SIGSEGV as it needs read
access to the altstack which is prohibited by the user-defined PKRU value.

Fix this by restoring altstack before restoring PKRU.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20240802061318.2140081-5-aruna.ramakrishna@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/x86/kernel/signal_64.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index 8a94053c54446..ee9453891901b 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -260,13 +260,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
 
 	set_current_blocked(&set);
 
-	if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
+	if (restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-	if (restore_signal_shadow_stack())
+	if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
 		goto badframe;
 
-	if (restore_altstack(&frame->uc.uc_stack))
+	if (restore_signal_shadow_stack())
 		goto badframe;
 
 	return regs->ax;
-- 
2.43.0