From: Eric Blake <eblake@redhat.com>
To: Warner Losh <imp@bsdimp.com>
Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>,
kvm-devel <kvm@vger.kernel.org>,
"Kyle Evans" <kevans@freebsd.org>,
"QEMU Developers" <qemu-devel@nongnu.org>,
qemu-arm <qemu-arm@nongnu.org>, qemu-ppc <qemu-ppc@nongnu.org>,
"Gerd Hoffmann" <kraxel@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Alex Bennée" <alex.bennee@linaro.org>
Subject: Re: [PATCH v2 4/9] bsd-user/syscall: Replace alloca() by g_new()
Date: Thu, 6 May 2021 10:42:50 -0500 [thread overview]
Message-ID: <adfc5da4-a615-24d7-0c67-f04d4eaec9a6@redhat.com> (raw)
In-Reply-To: <CANCZdfrcv9ZUcBv7z+z3JPCjy0uzzY07VLmC4dqr5r8ba_QPLw@mail.gmail.com>
On 5/6/21 10:30 AM, Warner Losh wrote:
>
> But for the real answer, I need to contact the original authors of
> this part of the code (they are no longer involved day-to-day in
> the bsd-user efforts) to see if this scenario is possible or not. If
> it's easy to find out that way, we can either know this is safe to
> do, or if effort is needed to make it safe. At present, I've seen
> enough and chatted enough with others to be concerned that
> the change would break proper emulation.
Do we have a feel for the maximum amount of memory being used by the
various alloca() replaced in this series? If so, can we just
stack-allocate an array of bytes of the maximum size needed? Then we
avoid alloca() but also avoid the dynamic memory management that
malloc() would introduce. Basically, it boils down to auditing why the
alloca() is safe, and once we know that, replacing the variable-sized
precise alloca() with its counterpart statically-sized array allocation,
at the expense of some wasted stack space when the runtime size does not
use the full compile-time maximum size.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
WARNING: multiple messages have this Message-ID (diff)
From: Eric Blake <eblake@redhat.com>
To: Warner Losh <imp@bsdimp.com>
Cc: kvm-devel <kvm@vger.kernel.org>,
"Kyle Evans" <kevans@freebsd.org>,
"QEMU Developers" <qemu-devel@nongnu.org>,
"Alex Bennée" <alex.bennee@linaro.org>,
qemu-arm <qemu-arm@nongnu.org>, qemu-ppc <qemu-ppc@nongnu.org>,
"Gerd Hoffmann" <kraxel@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: [PATCH v2 4/9] bsd-user/syscall: Replace alloca() by g_new()
Date: Thu, 6 May 2021 10:42:50 -0500 [thread overview]
Message-ID: <adfc5da4-a615-24d7-0c67-f04d4eaec9a6@redhat.com> (raw)
In-Reply-To: <CANCZdfrcv9ZUcBv7z+z3JPCjy0uzzY07VLmC4dqr5r8ba_QPLw@mail.gmail.com>
On 5/6/21 10:30 AM, Warner Losh wrote:
>
> But for the real answer, I need to contact the original authors of
> this part of the code (they are no longer involved day-to-day in
> the bsd-user efforts) to see if this scenario is possible or not. If
> it's easy to find out that way, we can either know this is safe to
> do, or if effort is needed to make it safe. At present, I've seen
> enough and chatted enough with others to be concerned that
> the change would break proper emulation.
Do we have a feel for the maximum amount of memory being used by the
various alloca() replaced in this series? If so, can we just
stack-allocate an array of bytes of the maximum size needed? Then we
avoid alloca() but also avoid the dynamic memory management that
malloc() would introduce. Basically, it boils down to auditing why the
alloca() is safe, and once we know that, replacing the variable-sized
precise alloca() with its counterpart statically-sized array allocation,
at the expense of some wasted stack space when the runtime size does not
use the full compile-time maximum size.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
next prev parent reply other threads:[~2021-05-06 15:43 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 13:37 [PATCH v2 0/9] misc: Replace alloca() by g_malloc() Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 13:37 ` [PATCH v2 1/9] audio/alsaaudio: Replace ALSA alloca() by malloc() equivalent Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 13:37 ` [PATCH v2 2/9] backends/tpm: Replace qemu_mutex_lock calls with QEMU_LOCK_GUARD Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 14:46 ` Stefan Berger
2021-05-06 15:07 ` Christophe de Dinechin
2021-05-06 15:07 ` Christophe de Dinechin
2021-05-06 13:37 ` [PATCH v2 3/9] backends/tpm: Replace g_alloca() by g_malloc() Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 14:46 ` Stefan Berger
2021-05-06 14:46 ` Stefan Berger
2021-05-06 13:37 ` [PATCH v2 4/9] bsd-user/syscall: Replace alloca() by g_new() Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 14:16 ` Warner Losh
2021-05-06 14:20 ` Peter Maydell
2021-05-06 14:20 ` Peter Maydell
2021-05-06 14:48 ` Warner Losh
2021-05-06 14:57 ` Philippe Mathieu-Daudé
2021-05-06 15:07 ` Warner Losh
2021-05-06 14:25 ` Eric Blake
2021-05-06 14:55 ` Warner Losh
2021-05-06 15:12 ` Eric Blake
2021-05-06 15:12 ` Eric Blake
2021-05-06 15:30 ` Warner Losh
2021-05-06 15:42 ` Eric Blake [this message]
2021-05-06 15:42 ` Eric Blake
2021-05-06 16:03 ` Peter Maydell
2021-05-06 16:03 ` Peter Maydell
2021-05-06 16:09 ` Warner Losh
2021-05-06 15:58 ` Peter Maydell
2021-05-06 15:58 ` Peter Maydell
2021-05-06 16:08 ` Warner Losh
2021-05-06 13:37 ` [PATCH v2 5/9] gdbstub: Constify GdbCmdParseEntry Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 13:37 ` [PATCH v2 6/9] gdbstub: Only call cmd_parse_params() with non-NULL command schema Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 19:21 ` Alex Bennée
2021-05-06 19:21 ` Alex Bennée
2021-05-06 13:37 ` [PATCH v2 7/9] gdbstub: Replace alloca() + memset(0) by g_new0() Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 19:22 ` Alex Bennée
2021-05-06 19:22 ` Alex Bennée
2021-05-06 13:37 ` [PATCH v2 8/9] hw/misc/pca9552: Replace g_newa() by g_new() Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 13:37 ` [PATCH v2 9/9] target/ppc/kvm: Replace alloca() by g_malloc() Philippe Mathieu-Daudé
2021-05-06 13:37 ` Philippe Mathieu-Daudé
2021-05-06 14:45 ` Greg Kurz
2021-05-06 14:45 ` Greg Kurz
2021-05-07 1:05 ` David Gibson
2021-05-07 1:05 ` David Gibson
2021-05-06 14:22 ` [PATCH v2 0/9] misc: " Warner Losh
2021-05-06 14:28 ` Eric Blake
2021-05-06 15:02 ` Warner Losh
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