linux-kernel - [RFC PATCH v1 0/1] binfmt

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Message-ID: <20240801170838.356177-1-jeffxu@google.com>
Date: Thu,  1 Aug 2024 17:08:32 +0000
From: jeffxu@...omium.org
To: akpm@...ux-foundation.org,
	keescook@...omium.org,
	jannh@...gle.com,
	sroettger@...gle.com,
	adhemerval.zanella@...aro.org,
	ojeda@...nel.org,
	adobriyan@...il.com
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	jorgelo@...omium.org,
	Jeff Xu <jeffxu@...omium.org>
Subject: [RFC PATCH v1 0/1] binfmt_elf: seal address zero

From: Jeff Xu <jeffxu@...omium.org>

In load_elf_binary as part of the execve(),  when the current
task’s personality has MMAP_PAGE_ZERO set, the kernel allocates
one page at address 0. According to the comment:

/* Why this, you ask???  Well SVr4 maps page 0 as read-only,
    and some applications "depend" upon this behavior.
    Since we do not have the power to recompile these, we
     emulate the SVr4 behavior. Sigh. */

At one point, Linus suggested removing this [1].

Sealing this is probably safe, the comment doesn’t say 
the app ever wanting to change the mapping to rwx. Sealing
also ensures that never happens.

[1] https://lore.kernel.org/lkml/CAHk-=whVa=nm_GW=NVfPHqcxDbWt4JjjK1YWb0cLjO4ZSGyiDA@mail.gmail.com/

Jeff Xu (1):
  binfmt_elf: mseal address zero

 fs/binfmt_elf.c    | 4 ++++
 include/linux/mm.h | 4 ++++
 mm/mseal.c         | 2 +-
 3 files changed, 9 insertions(+), 1 deletion(-)

-- 
2.46.0.rc1.232.g9752f9e123-goog