From: "Bae, Chang Seok" <chang.seok.bae@intel.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "bp@suse.de" <bp@suse.de>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@kernel.org" <mingo@kernel.org>,
"luto@kernel.org" <luto@kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"Brown, Len" <len.brown@intel.com>,
"Hansen, Dave" <dave.hansen@intel.com>,
"hjl.tools@gmail.com" <hjl.tools@gmail.com>,
"Dave.Martin@arm.com" <Dave.Martin@arm.com>,
"jannh@google.com" <jannh@google.com>,
"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
"carlos@redhat.com" <carlos@redhat.com>,
"Luck, Tony" <tony.luck@intel.com>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v8 5/6] x86/signal: Detect and prevent an alternate signal stack overflow
Date: Tue, 18 May 2021 20:53:18 +0000 [thread overview]
Message-ID: <8933FF62-4AE9-44E7-8A05-ACA5A91BBE28@intel.com> (raw)
In-Reply-To: <1955da4c211f4d4fbbf74a6b8bdae0f6@AcuMS.aculab.com>
On Apr 22, 2021, at 15:04, David Laight <David.Laight@ACULAB.COM> wrote:
> From: Bae, Chang Seok Sent: 22 April 2021 17:31
>>
>> On Apr 22, 2021, at 01:46, David Laight <David.Laight@ACULAB.COM> wrote:
>>> From: Chang S. Bae Sent: 22 April 2021 05:49
>>>>
>>>>
>>>> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
>>>> index 3f6a0fcaa10c..ae60f838ebb9 100644
>>>> --- a/include/linux/sched/signal.h
>>>> +++ b/include/linux/sched/signal.h
>>>> @@ -537,6 +537,17 @@ static inline int kill_cad_pid(int sig, int priv)
>>>> #define SEND_SIG_NOINFO ((struct kernel_siginfo *) 0)
>>>> #define SEND_SIG_PRIV ((struct kernel_siginfo *) 1)
>>>>
>>>> +static inline int __on_sig_stack(unsigned long sp)
>>>> +{
>>>> +#ifdef CONFIG_STACK_GROWSUP
>>>> + return sp >= current->sas_ss_sp &&
>>>> + sp - current->sas_ss_sp < current->sas_ss_size;
>>>> +#else
>>>> + return sp > current->sas_ss_sp &&
>>>> + sp - current->sas_ss_sp <= current->sas_ss_size;
>>>> +#endif
>>>> +}
>>>> +
>>>
>>> Those don't look different enough.
>>
>> The difference is on the SS_AUTODISARM flag check. This refactoring was
>> suggested as on_sig_stack() brought confusion [3].
>
> I was just confused by the #ifdef.
> Whether %sp points to the last item or the next space is actually
> independent of the stack direction.
> A stack might usually use pre-decrement and post-increment but it
> doesn't have to.
> The stack pointer can't be right at one end of the alt-stack
> area (because that is the address you'd use when you switch to it),
> and if you are any where near the other end you are hosed.
> So a common test:
> return (unsigned long)(sp - current->sas_ss_sp) < current->sas_ss_size;
> will always work.
>
> It isn't as though the stack pointer should be anywhere else
> other than the 'real' thread stack.
Thanks for the suggestion. Yes, this hunk can be made better like that. But I
would make this change as pure refactoring. Perhaps, follow up after this
series.
Chang
next prev parent reply other threads:[~2021-05-18 20:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 4:48 [PATCH v8 0/6] Improve Minimum Alternate Stack Size Chang S. Bae
2021-04-22 4:48 ` [PATCH v8 1/6] uapi: Define the aux vector AT_MINSIGSTKSZ Chang S. Bae
2021-04-22 4:48 ` [PATCH v8 2/6] x86/signal: Introduce helpers to get the maximum signal frame size Chang S. Bae
2021-05-03 13:06 ` Borislav Petkov
2021-04-22 4:48 ` [PATCH v8 3/6] x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ Chang S. Bae
2021-04-22 4:48 ` [PATCH v8 4/6] selftest/sigaltstack: Use the AT_MINSIGSTKSZ aux vector if available Chang S. Bae
2021-04-22 4:48 ` [PATCH v8 5/6] x86/signal: Detect and prevent an alternate signal stack overflow Chang S. Bae
2021-04-22 8:46 ` David Laight
2021-04-22 16:31 ` Bae, Chang Seok
2021-04-22 22:04 ` David Laight
2021-05-18 20:53 ` Bae, Chang Seok [this message]
2021-05-11 18:36 ` Borislav Petkov
2021-05-12 18:48 ` Bae, Chang Seok
2021-05-12 20:55 ` Thomas Gleixner
2021-05-14 7:26 ` Borislav Petkov
2021-04-22 4:48 ` [PATCH v8 6/6] selftest/x86/signal: Include test cases for validating sigaltstack Chang S. Bae
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