linux-kernel - Re: [PATCH] Arm: mm: ftrace: Only set text back to ro after kernel has been marked ro

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Date:   Tue, 5 Dec 2017 20:09:35 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Kees Cook <keescook@...omium.org>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Eric Anholt <eric@...olt.net>,
        Phil Elwell <phil@...pberrypi.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Matthias Reichl <hias@...us.com>,
        linux-rpi-kernel@...ts.infradead.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] Arm: mm: ftrace: Only set text back to ro after kernel
 has been marked ro

On Tue, Dec 05, 2017 at 11:35:59AM -0800, Kees Cook wrote:
> We don't _need_ to, but they're all contiguous, so the ro_perms array
> used by set_kernel_text_*() is actually only a single entry:
> 
> static struct section_perm ro_perms[] = {
>         /* Make kernel code and rodata RX (set RO). */
>         {
>                 .name   = "text/rodata RO",
>                 .start  = (unsigned long)_stext,
>                 .end    = (unsigned long)__init_begin,
> ...

Well, they may not be contiguous - it depends on DEBUG_ALIGN_RODATA.

Either way, we have __start_rodata_section_aligned, which is either
the start of the read-only data section, or the start of the first
section beyond __start_rodata if DEBUG_ALIGN_RODATA is not set.

Given that __start_rodata_section_aligned will always be less than
__init_begin, is there any reason not to make the above end at
__start_rodata_section_aligned, thereby allowing more of the read-only
data (in the case of DEBUG_ALIGN_RODATA=n) or all of the read-only
data (in the case of DEBUG_ALIGN_RODATA=y) to remain write-protected?

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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