From: Greg KH <gregkh@linuxfoundation.org>
To: Vaibhav Rustagi <vaibhavrustagi@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Vivek Goyal <vgoyal@redhat.com>,
Nick Desaulniers <ndesaulniers@google.com>,
stable@vger.kernel.org, Manoj Gupta <manojgupta@google.com>,
Alistair Delva <adelva@google.com>
Subject: Re: [PATCH 2/2] x86/purgatory: do not use __builtin_memcpy and __builtin_memset.
Date: Thu, 18 Jul 2019 09:47:15 +0900 [thread overview]
Message-ID: <20190718004715.GB31085@kroah.com> (raw)
In-Reply-To: <20190718000206.121392-3-vaibhavrustagi@google.com>
On Wed, Jul 17, 2019 at 05:02:06PM -0700, Vaibhav Rustagi wrote:
> From: Nick Desaulniers <ndesaulniers@google.com>
>
> 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
> if we define warn as a symbol.
>
> Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
> Reported-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> Tested-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: Vaibhav Rustagi <vaibhavrustagi@google.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> arch/x86/purgatory/Makefile | 3 +++
> arch/x86/purgatory/purgatory.c | 6 ++++++
> arch/x86/purgatory/string.c | 23 -----------------------
> 3 files changed, 9 insertions(+), 23 deletions(-)
> delete mode 100644 arch/x86/purgatory/string.c
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
next prev parent reply other threads:[~2019-07-18 0:47 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 0:02 [PATCH 0/2] Support kexec/kdump for clang built kernel Vaibhav Rustagi
2019-07-18 0:02 ` [PATCH 1/2] x86/purgatory: add -mno-sse, -mno-mmx, -mno-sse2 to Makefile Vaibhav Rustagi
2019-07-18 0:47 ` Greg KH
2019-07-18 21:34 ` Nick Desaulniers
2019-07-19 8:17 ` Peter Zijlstra
2019-07-22 21:12 ` Nick Desaulniers
2019-07-18 0:02 ` [PATCH 2/2] x86/purgatory: do not use __builtin_memcpy and __builtin_memset Vaibhav Rustagi
2019-07-18 0:47 ` Greg KH [this message]
2019-07-18 21:56 ` Nick Desaulniers
2019-07-18 21:29 ` [PATCH 0/2] Support kexec/kdump for clang built kernel Nick Desaulniers
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