From: Kees Cook <keescook@chromium.org>
To: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
Xuefeng Li <lixuefeng@loongson.cn>,
Juxin Gao <gaojuxin@loongson.cn>
Subject: Re: [PATCH] MIPS: Prevent READ_IMPLIES_EXEC propagation
Date: Wed, 8 Jul 2020 16:26:09 -0700 [thread overview]
Message-ID: <202007081624.82FA0CC1EA@keescook> (raw)
In-Reply-To: <1594114741-26852-1-git-send-email-yangtiezhu@loongson.cn>
On Tue, Jul 07, 2020 at 05:39:01PM +0800, Tiezhu Yang wrote:
> In the MIPS architecture, we should clear the security-relevant
> flag READ_IMPLIES_EXEC in the function SET_PERSONALITY2() of the
> file arch/mips/include/asm/elf.h.
>
> Otherwise, with this flag set, PROT_READ implies PROT_EXEC for
> mmap to make memory executable that is not safe, because this
> condition allows an attacker to simply jump to and execute bytes
> that are considered to be just data [1].
>
> In mm/mmap.c:
> unsigned long do_mmap(struct file *file, unsigned long addr,
> unsigned long len, unsigned long prot,
> unsigned long flags, vm_flags_t vm_flags,
> unsigned long pgoff, unsigned long *populate,
> struct list_head *uf)
> {
> [...]
> if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
> if (!(file && path_noexec(&file->f_path)))
> prot |= PROT_EXEC;
> [...]
> }
>
> By the way, x86 and ARM64 have done the similar thing.
>
> After commit 250c22777fe1 ("x86_64: move kernel"), in the file
> arch/x86/kernel/process_64.c:
> void set_personality_64bit(void)
> {
> [...]
> current->personality &= ~READ_IMPLIES_EXEC;
> }
>
> After commit 48f99c8ec0b2 ("arm64: Preventing READ_IMPLIES_EXEC
> propagation"), in the file arch/arm64/include/asm/elf.h:
> #define SET_PERSONALITY(ex) \
> ({ \
> clear_thread_flag(TIF_32BIT); \
> current->personality &= ~READ_IMPLIES_EXEC; \
> })
>
> [1] https://insights.sei.cmu.edu/cert/2014/02/feeling-insecure-blame-your-parent.html
>
> Reported-by: Juxin Gao <gaojuxin@loongson.cn>
> Co-developed-by: Juxin Gao <gaojuxin@loongson.cn>
> Signed-off-by: Juxin Gao <gaojuxin@loongson.cn>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
This seems correct to me.
Reviewed-by: Kees Cook <keescook@chromium.org>
BTW, does MIPS also need similar changes to this series:
https://lore.kernel.org/lkml/20200327064820.12602-1-keescook@chromium.org/
Quoting from there "MIPS may need adjusting but the history of CPU
features and toolchain behavior is very unclear to me."
--
Kees Cook
next prev parent reply other threads:[~2020-07-08 23:26 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 9:39 [PATCH] MIPS: Prevent READ_IMPLIES_EXEC propagation Tiezhu Yang
2020-07-07 19:45 ` Maciej W. Rozycki
2020-07-08 7:51 ` Tiezhu Yang
2020-07-17 10:00 ` Maciej W. Rozycki
2020-07-18 0:04 ` YunQiang Su
2020-07-18 3:59 ` Tiezhu Yang
2020-07-18 4:45 ` YunQiang Su
2020-07-08 23:26 ` Kees Cook [this message]
2020-07-16 11:59 ` Thomas Bogendoerfer
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