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From: Catalin Marinas <catalin.marinas@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Hector Marco-Gisbert <hecmargi@upv.es>,
	Will Deacon <will.deacon@arm.com>,
	Jason Gunthorpe <jgg@mellanox.com>, Jann Horn <jannh@google.com>,
	Russell King <linux@armlinux.org.uk>,
	x86@kernel.org, kernel-hardening@lists.openwall.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 5/7] arm32/64, elf: Split READ_IMPLIES_EXEC from executable GNU_STACK
Date: Wed, 12 Feb 2020 09:27:39 +0000
Message-ID: <20200212092739.GC488264@arrakis.emea.arm.com> (raw)
In-Reply-To: <20200210193049.64362-6-keescook@chromium.org>

On Mon, Feb 10, 2020 at 11:30:47AM -0800, Kees Cook wrote:
> The READ_IMPLIES_EXEC work-around was designed for old toolchains that
> lacked the ELF PT_GNU_STACK marking under the assumption that toolchains
> that couldn't specify executable permission flags for the stack may not
> know how to do it correctly for any memory region.
> 
> This logic is sensible for having ancient binaries coexist in a system
> with possibly NX memory, but was implemented in a way that equated having
> a PT_GNU_STACK marked executable as being as "broken" as lacking the
> PT_GNU_STACK marking entirely. Things like unmarked assembly and stack
> trampolines may cause PT_GNU_STACK to need an executable bit, but they
> do not imply all mappings must be executable.
> 
> This confusion has led to situations where modern programs with explicitly
> marked executable stack are forced into the READ_IMPLIES_EXEC state when
> no such thing is needed. (And leads to unexpected failures when mmap()ing
> regions of device driver memory that wish to disallow VM_EXEC[1].)
> 
> In looking for other reasons for the READ_IMPLIES_EXEC behavior, Jann
> Horn noted that glibc thread stacks have always been marked RWX (until
> 2003 when they started tracking the PT_GNU_STACK flag instead[2]). And
> musl doesn't support executable stacks at all[3]. As such, no breakage
> for multithreaded applications is expected from this change.
> 
> This changes arm32 and arm64 compat together, to keep behavior the same.
> 
> [1] https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com
> [2] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=54ee14b3882
> [3] https://lkml.kernel.org/r/20190423192534.GN23599@brightrain.aerifal.cx
> 
> Suggested-by: Hector Marco-Gisbert <hecmargi@upv.es>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-10 19:30 [PATCH v3 0/7] binfmt_elf: Update READ_IMPLIES_EXEC logic for modern CPUs Kees Cook
2020-02-10 19:30 ` [PATCH v3 1/7] x86/elf: Add table to document READ_IMPLIES_EXEC Kees Cook
2020-02-10 19:30 ` [PATCH v3 2/7] x86/elf: Split READ_IMPLIES_EXEC from executable GNU_STACK Kees Cook
2020-02-10 19:30 ` [PATCH v3 3/7] x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces Kees Cook
2020-02-10 19:30 ` [PATCH v3 4/7] arm32/64, elf: Add tables to document READ_IMPLIES_EXEC Kees Cook
2020-02-12  9:27   ` Catalin Marinas
2020-02-10 19:30 ` [PATCH v3 5/7] arm32/64, elf: Split READ_IMPLIES_EXEC from executable GNU_STACK Kees Cook
2020-02-12  9:27   ` Catalin Marinas [this message]
2020-02-10 19:30 ` [PATCH v3 6/7] arm64, elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces Kees Cook
2020-02-12  9:28   ` Catalin Marinas
2020-02-10 19:30 ` [PATCH v3 7/7] selftests/exec: Add READ_IMPLIES_EXEC tests Kees Cook
2020-02-11 18:11   ` shuah
2020-02-11 19:25     ` Kees Cook
2020-02-11 21:06       ` shuah
2020-02-11 23:54         ` Kees Cook
2020-02-12  0:02           ` shuah
2020-02-11 17:17 ` [PATCH v3 0/7] binfmt_elf: Update READ_IMPLIES_EXEC logic for modern CPUs Jason Gunthorpe

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