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From: "H.J. Lu" <hjl.tools@gmail.com>
To: Dave Martin <Dave.Martin@arm.com>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
	Andy Lutomirski <luto@kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Len Brown <len.brown@intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Tony Luck <tony.luck@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	GNU C Library <libc-alpha@sourceware.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size
Date: Mon, 5 Oct 2020 14:17:06 -0700
Message-ID: <CAMe9rOpZm43aDG3UJeaioU32zSYdTxQ=ZyZuSS4u0zjbs9RoKw@mail.gmail.com> (raw)
In-Reply-To: <20201005134534.GT6642@arm.com>

On Mon, Oct 5, 2020 at 6:45 AM Dave Martin <Dave.Martin@arm.com> wrote:
>
> On Tue, Sep 29, 2020 at 01:57:42PM -0700, Chang S. Bae wrote:
> > During signal entry, the kernel pushes data onto the normal userspace
> > stack. On x86, the data pushed onto the user stack includes XSAVE state,
> > which has grown over time as new features and larger registers have been
> > added to the architecture.
> >
> > MINSIGSTKSZ is a constant provided in the kernel signal.h headers and
> > typically distributed in lib-dev(el) packages, e.g. [1]. Its value is
> > compiled into programs and is part of the user/kernel ABI. The MINSIGSTKSZ
> > constant indicates to userspace how much data the kernel expects to push on
> > the user stack, [2][3].
> >
> > However, this constant is much too small and does not reflect recent
> > additions to the architecture. For instance, when AVX-512 states are in
> > use, the signal frame size can be 3.5KB while MINSIGSTKSZ remains 2KB.
> >
> > The bug report [4] explains this as an ABI issue. The small MINSIGSTKSZ can
> > cause user stack overflow when delivering a signal.
> >
> > In this series, we suggest a couple of things:
> > 1. Provide a variable minimum stack size to userspace, as a similar
> >    approach to [5]
> > 2. Avoid using a too-small alternate stack
>
> I can't comment on the x86 specifics, but the approach followed in this
> series does seem consistent with the way arm64 populates
> AT_MINSIGSTKSZ.
>
> I need to dig up my glibc hacks for providing a sysconf interface to
> this...

Here is my proposal for glibc:

https://sourceware.org/pipermail/libc-alpha/2020-September/118098.html

1. Define SIGSTKSZ and MINSIGSTKSZ to 64KB.
2. Add _SC_RSVD_SIG_STACK_SIZE for signal stack size reserved by the kernel.
3. Deprecate SIGSTKSZ and MINSIGSTKSZ if _SC_RSVD_SIG_STACK_SIZE
is in use.


-- 
H.J.

  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-29 20:57 Chang S. Bae
2020-09-29 20:57 ` [RFC PATCH 1/4] x86/signal: Introduce helpers to get the maximum signal frame size Chang S. Bae
2020-10-05 13:42   ` Dave Martin
2020-10-06 17:45     ` Bae, Chang Seok
2020-10-07 10:05       ` Dave Martin
2020-10-08 22:43         ` Bae, Chang Seok
2020-10-12 13:26           ` Dave Martin
2020-09-29 20:57 ` [RFC PATCH 2/4] x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ Chang S. Bae
2020-09-29 20:57 ` [RFC PATCH 3/4] x86/signal: Prevent an alternate stack overflow before a signal delivery Chang S. Bae
2020-09-29 20:57 ` [RFC PATCH 4/4] selftest/x86/signal: Include test cases for validating sigaltstack Chang S. Bae
2020-10-05 13:45 ` [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size Dave Martin
2020-10-05 21:17   ` H.J. Lu [this message]
2020-10-06  9:25     ` Dave Martin
2020-10-06 12:12       ` H.J. Lu
2020-10-06 15:18         ` H.J. Lu
2020-10-06 15:43           ` Dave Martin
2020-10-06 16:52             ` H.J. Lu
2020-10-06 15:25         ` Dave Martin
2020-10-06 15:33           ` Dave Hansen
2020-10-06 17:00             ` Dave Martin
2020-10-06 18:21               ` Florian Weimer
2020-10-07 10:19                 ` Dave Martin
2020-10-06 18:30               ` Dave Hansen
2020-10-07 10:20                 ` Dave Martin
2020-10-06 15:34           ` H.J. Lu
2020-10-06 16:55             ` Dave Martin
2020-10-06 17:44               ` H.J. Lu
2020-10-07 10:47                 ` Dave Martin
2020-10-07 13:30                   ` H.J. Lu
2020-10-07 15:45                     ` Dave Martin
2020-10-07 17:43                       ` H.J. Lu

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