From: Dave Martin <Dave.Martin@arm.com>
To: linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org, Kees Cook <keescook@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: [RFC PATCH 0/2] ELF: Alternate program property parser
Date: Tue, 20 Aug 2019 10:57:41 +0100 [thread overview]
Message-ID: <1566295063-7387-1-git-send-email-Dave.Martin@arm.com> (raw)
This series is an experimental reimplementation of ELF property parsing
(see NT_GNU_PROPERTY_TYPE_0, [1]) for the ELF loader.
This is intended for comparison / merging with [2] (or could replace it,
if people think this approach is better).
Either way, I'd like to get something in place so that we can build
AArch64 BTI support on top of it.
Any thoughts?
Key differences from [2]:
* Scanning for the PT_PROGRAM_PROPERTY program header is intergrated
into the existing scan loops, rather than being done separately.
* In keeping with the rest of the ELF loader code, error checks are
kept to a minimum. Except to avoid buffer overruns, the ELF file is
not checked for well-formedness.
As a sanity check, the code still checks for a correct
NT_GNU_PROPERTY_TYPE_0 note header at the start of the
PT_PROGRAM_PROPERTY segment, but perhaps this isn't needed either.
* 1K is statically allocated on the stack for the properties, and if
the ELF properties are larger than that, the ELF file is rejected
with ENOEXEC.
There is no limit defined in [1] for the total size of the
properties, but common sense seems suggests that 1K is likely to be
ample space.
* The properties are found, read and parsed exactly once. [2] does
this once _per property_ requested by the arch code: that's not a
problem today, but it will become inefficient with there are multiple
properties in the file that the kernel needs to look at.
Instead, the arch arch_parse_elf_property() hook is called once per
property found. To minimise overhead, the arch code can implement
this hook inline.
This approach assumes that the number of properties in a given ELF is
say, no more than 20 or so. The code could be redesigned in the
future if/when this iteration becomes an overhead (i.e., probably
never).
[1] Linux Extensions to gABI
https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI
[2] [PATCH v8 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file
https://lore.kernel.org/lkml/20190813205225.12032-23-yu-cheng.yu@intel.com/
Dave Martin (2):
ELF: UAPI and Kconfig additions for ELF program properties
ELF: Add ELF program property parsing support
fs/Kconfig.binfmt | 3 ++
fs/binfmt_elf.c | 109 +++++++++++++++++++++++++++++++++++++++++++++++
fs/compat_binfmt_elf.c | 4 ++
include/linux/elf.h | 21 +++++++++
include/uapi/linux/elf.h | 11 +++++
5 files changed, 148 insertions(+)
--
2.1.4
next reply other threads:[~2019-08-20 9:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-20 9:57 Dave Martin [this message]
2019-08-20 9:57 ` [RFC PATCH 1/2] ELF: UAPI and Kconfig additions for ELF program properties Dave Martin
2019-08-20 9:57 ` [RFC PATCH 2/2] ELF: Add ELF program property parsing support Dave Martin
2019-08-20 21:40 ` Yu-cheng Yu
2019-08-21 9:20 ` Dave Martin
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