From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
csky restore_sigcontext() blindly overwrites regs->sr with the value
it finds in sigcontext. Attacker can store whatever they want in there,
which includes things like S-bit. Userland shouldn't be able to set
that, or anything other than C flag (bit 0).
Do the same thing other architectures with protected bits in flags
register do - preserve everything that shouldn't be settable in
user mode, picking the rest from the value saved is sigcontext.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
arch/csky/kernel/signal.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
index 312f046d452d..6ba3969ec175 100644
--- a/arch/csky/kernel/signal.c
+++ b/arch/csky/kernel/signal.c
@@ -52,10 +52,14 @@ static long restore_sigcontext(struct pt_regs *regs,
struct sigcontext __user *sc)
{
int err = 0;
+ unsigned long sr = regs->sr;
/* sc_pt_regs is structured the same as the start of pt_regs */
err |= __copy_from_user(regs, &sc->sc_pt_regs, sizeof(struct pt_regs));
+ /* BIT(0) of regs->sr is Condition Code/Carry bit */
+ regs->sr = (sr & ~1) | (regs->sr & 1);
+
/* Restore the floating-point state. */
err |= restore_fpu_state(sc);
--
2.25.1
