From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Sami Tolvanen <samitolvanen@google.com>,
Mark Rutland <mark.rutland@arm.com>,
"Mohan Rao .vanimina" <mailtoc.mohanrao@gmail.com>,
Nathan Chancellor <nathan@kernel.org>
Subject: Re: [PATCH] vmlinux.lds.h: CFI: Reduce alignment of jump-table to function alignment
Date: Thu, 22 Sep 2022 15:18:01 -0700 [thread overview]
Message-ID: <202209221514.B2B02622@keescook> (raw)
In-Reply-To: <20220922215715.13345-1-will@kernel.org>
On Thu, Sep 22, 2022 at 10:57:15PM +0100, Will Deacon wrote:
> Due to undocumented, hysterical raisins on x86, the CFI jump-table
> sections in .text are needlessly aligned to PMD_SIZE in the vmlinux
> linker script. When compiling a CFI-enabled arm64 kernel with a 64KiB
> page-size, a PMD maps 512MiB of virtual memory and so the .text section
> increases to a whopping 940MiB and blows the final Image up to 960MiB.
> Others report a link failure.
Heh. "That's not an image ... THIS is an image."[1]
> Since the CFI jump-table requires only instruction alignment, reduce the
> alignment directives to function alignment for parity with other parts
> of the .text section. This reduces the size of the .text section for the
> aforementioned 64KiB page size arm64 kernel to 19MiB for a much more
> reasonable total Image size of 39MiB.
❤️
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
[1] https://www.youtube.com/watch?v=rne8pOxGuwM#t=27
--
Kees Cook
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WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Sami Tolvanen <samitolvanen@google.com>,
Mark Rutland <mark.rutland@arm.com>,
"Mohan Rao .vanimina" <mailtoc.mohanrao@gmail.com>,
Nathan Chancellor <nathan@kernel.org>
Subject: Re: [PATCH] vmlinux.lds.h: CFI: Reduce alignment of jump-table to function alignment
Date: Thu, 22 Sep 2022 15:18:01 -0700 [thread overview]
Message-ID: <202209221514.B2B02622@keescook> (raw)
In-Reply-To: <20220922215715.13345-1-will@kernel.org>
On Thu, Sep 22, 2022 at 10:57:15PM +0100, Will Deacon wrote:
> Due to undocumented, hysterical raisins on x86, the CFI jump-table
> sections in .text are needlessly aligned to PMD_SIZE in the vmlinux
> linker script. When compiling a CFI-enabled arm64 kernel with a 64KiB
> page-size, a PMD maps 512MiB of virtual memory and so the .text section
> increases to a whopping 940MiB and blows the final Image up to 960MiB.
> Others report a link failure.
Heh. "That's not an image ... THIS is an image."[1]
> Since the CFI jump-table requires only instruction alignment, reduce the
> alignment directives to function alignment for parity with other parts
> of the .text section. This reduces the size of the .text section for the
> aforementioned 64KiB page size arm64 kernel to 19MiB for a much more
> reasonable total Image size of 39MiB.
❤️
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
[1] https://www.youtube.com/watch?v=rne8pOxGuwM#t=27
--
Kees Cook
next prev parent reply other threads:[~2022-09-22 22:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-22 21:57 [PATCH] vmlinux.lds.h: CFI: Reduce alignment of jump-table to function alignment Will Deacon
2022-09-22 21:57 ` Will Deacon
2022-09-22 22:00 ` Sami Tolvanen
2022-09-22 22:00 ` Sami Tolvanen
2022-09-22 22:18 ` Kees Cook [this message]
2022-09-22 22:18 ` Kees Cook
2022-09-23 12:24 ` Mark Rutland
2022-09-23 12:24 ` Mark Rutland
2022-09-23 15:40 ` Will Deacon
2022-09-23 15:40 ` Will Deacon
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