From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Finn Thain <fthain@linux-m68k.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
"Christopher M. Riedl" <cmr@bluescreens.de>
Subject: Re: [PATCH] powerpc: Fix sigset_t copy
Date: Wed, 10 Nov 2021 18:12:10 +0100 [thread overview]
Message-ID: <ed04d4a1-7a60-ee39-f64b-203b299e8875@csgroup.eu> (raw)
In-Reply-To: <08bbe7240b384016e0b2912ecf3bf5e2d25ef2c6.1636501628.git.fthain@linux-m68k.org>
Le 10/11/2021 à 00:47, Finn Thain a écrit :
> From: Christophe Leroy <christophe.leroy@csgroup.eu>
>
> The conversion from __copy_from_user() to __get_user() introduced a
> regression in __get_user_sigset() in v5.13. The bug was subsequently
> copied and pasted in unsafe_get_user_sigset().
>
> 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 casting the __get_user() assignment lvalue to u64
> so that the entire struct gets copied.
>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Cc: Christopher M. Riedl <cmr@bluescreens.de>
> Link: https://lore.kernel.org/linuxppc-dev/FEtBUOuFPMN4zJy4bIOqz6C4xoliCbTxS7VtMKD6UZkbvEbycUceRgGAd7e9-trRdwVN3hWAbQi0qrNx8Zgn8niTQf2KPVdw-W35czDIaeQ=@protonmail.com/
> Fixes: 887f3ceb51cd ("powerpc/signal32: Convert do_setcontext[_tm]() to user access block")
> Fixes: d3ccc9781560 ("powerpc/signal: Use __get_user() to copy sigset_t")
> Reported-and-tested-by: Stan Johnson <userm57@yahoo.com>
> Signed-off-by: Finn Thain <fthain@linux-m68k.org>
> ---
Hi Finn,
> Christophe, I hope this change is the one you wanted to see upstream (?).
> If it is acceptable please add your signed-off-by tag.
I'm on holidays, I was planing to handle this next week.
Only PPC64 uses __get_user_sigset() on mainline so I don't think it is
worth modifying it. If we decide to modify it anyway in mainline, it
should be another patch that can be backported without additional effort.
For unsafe_get_user_sigset(), as we don't have the KUAP overhead that we
had with __get_user(), I'd prefer we simply perform two 32 bits
unsafe_get_user(), one for sig[0] and one for sig[1], instead of all
those casts to u64.
Thanks anyway for the detailed description of the problem.
Christophe
> ---
> arch/powerpc/kernel/signal.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> index 1f07317964e4..44e736b88e91 100644
> --- a/arch/powerpc/kernel/signal.h
> +++ b/arch/powerpc/kernel/signal.h
> @@ -23,10 +23,10 @@ static inline int __get_user_sigset(sigset_t *dst, const sigset_t __user *src)
> {
> BUILD_BUG_ON(sizeof(sigset_t) != sizeof(u64));
>
> - return __get_user(dst->sig[0], (u64 __user *)&src->sig[0]);
> + return __get_user(*(u64 *)&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)
> + unsafe_get_user(*(u64 *)&(dst)->sig[0], (u64 __user *)&(src)->sig[0], label)
>
> #ifdef CONFIG_VSX
> extern unsigned long copy_vsx_to_user(void __user *to,
>
next prev parent reply other threads:[~2021-11-10 17:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-09 23:47 [PATCH] powerpc: Fix sigset_t copy Finn Thain
2021-11-10 17:12 ` Christophe Leroy [this message]
2021-11-11 0:20 ` Finn Thain
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