From: Greg KH <gregkh@linuxfoundation.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: adelva@google.com, manojgupta@google.com, tglx@linutronix.de,
vaibhavrustagi@google.com, stable@vger.kernel.org
Subject: Re: [4.19 PATCH] x86/purgatory: Do not use __builtin_memcpy and __builtin_memset
Date: Wed, 14 Aug 2019 10:04:39 +0200 [thread overview]
Message-ID: <20190814080439.GA28460@kroah.com> (raw)
In-Reply-To: <20190813211930.42094-1-ndesaulniers@google.com>
On Tue, Aug 13, 2019 at 02:19:30PM -0700, Nick Desaulniers wrote:
> commit 4ce97317f41d38584fb93578e922fcd19e535f5b upstream.
>
> Implementing memcpy and memset in terms of __builtin_memcpy and
> __builtin_memset is problematic.
>
> GCC at -O2 will replace calls to the builtins with calls to memcpy and
> memset (but will generate an inline implementation at -Os). Clang will
> replace the builtins with these calls regardless of optimization level.
> $ llvm-objdump -dr arch/x86/purgatory/string.o | tail
>
> 0000000000000339 memcpy:
> 339: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax
> 000000000000033b: R_X86_64_64 memcpy
> 343: ff e0 jmpq *%rax
>
> 0000000000000345 memset:
> 345: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax
> 0000000000000347: R_X86_64_64 memset
> 34f: ff e0
>
> Such code results in infinite recursion at runtime. This is observed
> when doing kexec.
>
> Instead, reuse an implementation from arch/x86/boot/compressed/string.c.
> This requires to implement a stub function for warn(). Also, Clang may
> lower memcmp's that compare against 0 to bcmp's, so add a small definition,
> too. See also: commit 5f074f3e192f ("lib/string.c: implement a basic bcmp")
>
> Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality")
> Reported-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> Debugged-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> Debugged-by: Manoj Gupta <manojgupta@google.com>
> Suggested-by: Alistair Delva <adelva@google.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> Cc: stable@vger.kernel.org
> Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
> Link: https://lkml.kernel.org/r/20190807221539.94583-1-ndesaulniers@google.com
> ---
> This failed to cherry-pick back cleanly due to the SPDX license
> identifier not existing in arch/x86/purgatory/string.c in 4.19. `git rm`
> it anyway.
Now queued up, thanks.
So the Fixes: tag does not mean this should be backported to anything
older? It implies this bug has been in the kernel since the 3.17
release.
thanks,
greg k-h
next prev parent reply other threads:[~2019-08-14 8:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 18:40 FAILED: patch "[PATCH] x86/purgatory: Do not use __builtin_memcpy and" failed to apply to 4.19-stable tree gregkh
2019-08-13 21:19 ` [4.19 PATCH] x86/purgatory: Do not use __builtin_memcpy and __builtin_memset Nick Desaulniers
2019-08-14 8:04 ` Greg KH [this message]
2019-08-14 20:41 ` Nick Desaulniers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190814080439.GA28460@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=adelva@google.com \
--cc=manojgupta@google.com \
--cc=ndesaulniers@google.com \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=vaibhavrustagi@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).