The conversion from __copy_from_user() to __get_user() by
commit d3ccc9781560 ("powerpc/signal: Use __get_user() to copy
sigset_t") introduced a regression in __get_user_sigset() for
powerpc/32. The bug was subsequently moved into
unsafe_get_user_sigset().
The bug is due to the copied 64 bit value being truncated to
32 bits while being assigned to dst->sig[0]
The regression was reported by users of the Xorg packages distributed in
Debian/powerpc --
"The symptoms are that the fb screen goes blank, with the backlight
remaining on and no errors logged in /var/log; wdm (or startx) run
with no effect (I tried logging in in the blind, with no effect).
And they are hard to kill, requiring 'kill -KILL ...'"
Fix the regression by copying each word of the sigset, not only the
first one.
__get_user_sigset() was tentatively optimised to copy 64 bits at once
in order to minimise KUAP unlock/lock impact, but the unsafe variant
doesn't suffer that, so it can just copy words.
Cc: Christopher M. Riedl <[email protected]>
Fixes: 887f3ceb51cd ("powerpc/signal32: Convert do_setcontext[_tm]() to user access block")
Cc: [email protected]
Reported-by: Finn Thain <[email protected]>
Reported-and-tested-by: Stan Johnson <[email protected]>
Signed-off-by: Christophe Leroy <[email protected]>
---
arch/powerpc/kernel/signal.h | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
index 1f07317964e4..618aeccdf691 100644
--- a/arch/powerpc/kernel/signal.h
+++ b/arch/powerpc/kernel/signal.h
@@ -25,8 +25,14 @@ static inline int __get_user_sigset(sigset_t *dst, const sigset_t __user *src)
return __get_user(dst->sig[0], (u64 __user *)&src->sig[0]);
}
-#define unsafe_get_user_sigset(dst, src, label) \
- unsafe_get_user((dst)->sig[0], (u64 __user *)&(src)->sig[0], label)
+#define unsafe_get_user_sigset(dst, src, label) do { \
+ sigset_t *__dst = dst; \
+ const sigset_t __user *__src = src; \
+ int i; \
+ \
+ for (i = 0; i < _NSIG_WORDS; i++) \
+ unsafe_get_user(__dst->sig[i], &__src->sig[i], label); \
+} while (0)
#ifdef CONFIG_VSX
extern unsigned long copy_vsx_to_user(void __user *to,
--
2.31.1
On Mon, 15 Nov 2021 09:52:55 +0100, Christophe Leroy wrote:
> The conversion from __copy_from_user() to __get_user() by
> commit d3ccc9781560 ("powerpc/signal: Use __get_user() to copy
> sigset_t") introduced a regression in __get_user_sigset() for
> powerpc/32. The bug was subsequently moved into
> unsafe_get_user_sigset().
>
> The bug is due to the copied 64 bit value being truncated to
> 32 bits while being assigned to dst->sig[0]
>
> [...]
Applied to powerpc/fixes.
[1/1] powerpc/signal32: Fix sigset_t copy
https://git.kernel.org/powerpc/c/5499802b2284331788a440585869590f1bd63f7f
cheers