From: Daniel Axtens <dja@axtens.net>
To: "Michal Suchánek" <msuchanek@suse.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
linuxppc-dev@lists.ozlabs.org,
Daniel Black <daniel@linux.ibm.com>
Subject: Re: [PATCH] powerpc/fault: kernel can extend a user process's stack
Date: Wed, 11 Dec 2019 20:37:21 +1100 [thread overview]
Message-ID: <8736drciem.fsf@dja-thinkpad.axtens.net> (raw)
In-Reply-To: <20191211072806.GI3986@kitsune.suse.cz>
> Fixes: 14cf11af6cf6 ("powerpc: Merge enough to start building in
> arch/powerpc.")
Wow, that's pretty ancient! I'm also not sure it's right - in that same
patch, arch/ppc64/mm/fault.c contains:
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 213) if (address + 2048 < uregs->gpr[1]
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 214) && (!user_mode(regs) || !store_updates_sp(regs)))
^1da177e4c3f4 (Linus Torvalds 2005-04-16 15:20:36 -0700 215) goto bad_area;
Which is the same as the new arch/powerpc/mm/fault.c code:
14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 234) if (address + 2048 < uregs->gpr[1]
14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 235) && (!user_mode(regs) || !store_updates_sp(regs)))
14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 236) goto bad_area;
So either they're both right or they're both wrong, either way I'm not
sure how this patch is to blame.
I guess we should also cc stable@...
Regards,
Daniel
>> Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
>> Cc: Daniel Black <daniel@linux.ibm.com>
>> Signed-off-by: Daniel Axtens <dja@axtens.net>
>> ---
>> arch/powerpc/mm/fault.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>> index b5047f9b5dec..00183731ea22 100644
>> --- a/arch/powerpc/mm/fault.c
>> +++ b/arch/powerpc/mm/fault.c
>> @@ -287,7 +287,17 @@ static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
>> if (!res)
>> return !store_updates_sp(inst);
>> *must_retry = true;
>> + } else if ((flags & FAULT_FLAG_WRITE) &&
>> + !(flags & FAULT_FLAG_USER)) {
>> + /*
>> + * the kernel can also attempt to write beyond the end
>> + * of a process's stack - for example setting up a
>> + * signal frame. We assume this is valid, subject to
>> + * the checks in expand_stack() later.
>> + */
>> + return false;
>> }
>> +
>> return true;
>> }
>> return false;
>> --
>> 2.20.1
>>
next prev parent reply other threads:[~2019-12-11 9:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 1:43 [PATCH] powerpc/fault: kernel can extend a user process's stack Daniel Axtens
2019-12-11 6:14 ` Daniel Black
2019-12-11 7:28 ` Michal Suchánek
2019-12-11 9:37 ` Daniel Axtens [this message]
2020-07-20 10:51 ` Michal Suchánek
2020-07-20 13:52 ` Michael Ellerman
2020-07-21 0:57 ` Daniel Axtens
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