From: Al Viro viro@zeniv.linux.org.uk

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@zeniv.linux.org.uk Signed-off-by: Guo Ren guoren@kernel.org Cc: stable@vger.kernel.org --- 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);