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: Thu, 22 Apr 2021 16:31:26 +0000 [thread overview]
Message-ID: <9C452E66-0C41-462B-9971-56825444AD65@intel.com> (raw)
In-Reply-To: <854d6aefdf604b559e37e82669b5e67f@AcuMS.aculab.com>
On Apr 22, 2021, at 01:46, David Laight <David.Laight@ACULAB.COM> wrote:
> From: Chang S. Bae
>> Sent: 22 April 2021 05:49
>>
>> The kernel pushes context on to the userspace stack to prepare for the
>> user's signal handler. When the user has supplied an alternate signal
>> stack, via sigaltstack(2), it is easy for the kernel to verify that the
>> stack size is sufficient for the current hardware context.
>>
>> Check if writing the hardware context to the alternate stack will exceed
>> it's size. If yes, then instead of corrupting user-data and proceeding with
>> the original signal handler, an immediate SIGSEGV signal is delivered.
>
> What happens if SIGSEGV is caught?
Boris pointed out the relevant notes before [1]. I think "unpredictable
results" is a somewhat vague statement but process termination is unavoidable
in this situation.
In the thread [1], a new signal number was discussed for the signal delivery
failure, but my takeaway is this SIGSEGV is still recognizable.
FWIW, Len summarized other possible approaches as well [2].
>> Refactor the stack pointer check code from on_sig_stack() and use the new
>> helper.
>>
>> While the kernel allows new source code to discover and use a sufficient
>> alternate signal stack size, this check is still necessary to protect
>> binaries with insufficient alternate signal stack size from data
>> corruption.
> ...
>> 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].
Thanks,
Chang
[1] https://lore.kernel.org/lkml/20210414120608.GE10709@zn.tnic/
[2] https://lore.kernel.org/lkml/CAJvTdKnpWL8y4N_BrCiK7fU0UXERwuuM8o84LUpp7Watxd8STw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/20210325212733.GC32296@zn.tnic/
next prev parent reply other threads:[~2021-04-22 16:32 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 [this message]
2021-04-22 22:04 ` David Laight
2021-05-18 20:53 ` Bae, Chang Seok
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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