Date: Wed, 2 Dec 2015 16:05:06 -0800 From: Laura Abbott <labbott@...hat.com> To: Kees Cook <keescook@...omium.org> Cc: Laura Abbott <labbott@...oraproject.org>, Russell King <linux@....linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, linux-arm-kernel@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Will Deacon <will.deacon@....com>, Nicolas Pitre <nico@...aro.org>, Arnd Bergmann <arnd@...db.de>, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH v2] ARM: mm: flip priority of CONFIG_DEBUG_RODATA On 12/02/2015 12:27 PM, Kees Cook wrote: > The use of CONFIG_DEBUG_RODATA is generally seen as an essential part of > kernel self-protection: > http://www.openwall.com/lists/kernel-hardening/2015/11/30/13 > Additionally, its name has grown to mean things beyond just rodata. To > get ARM closer to this, we ought to rearrange the names of the configs > that control how the kernel protects its memory. What was called > CONFIG_ARM_KERNMEM_PERMS is really doing the work that other architectures > call CONFIG_DEBUG_RODATA. > > This redefines CONFIG_DEBUG_RODATA to actually do the bulk of the > ROing (and NXing). In the place of the old CONFIG_DEBUG_RODATA, use > CONFIG_DEBUG_ALIGN_RODATA, since that's what the option does: adds > section alignment for making rodata explicitly NX, as arm does not split > the page tables like arm64 does without _ALIGN_RODATA. > > Also adds human readable names to the sections so I could more easily > debug my typos, and makes CONFIG_DEBUG_RODATA default "y" for CPU_V7. > > Results in /sys/kernel/debug/kernel_page_tables for each config state: > > # CONFIG_DEBUG_RODATA is not set > # CONFIG_DEBUG_ALIGN_RODATA is not set > > ---[ Kernel Mapping ]--- > 0x80000000-0x80900000 9M RW x SHD > 0x80900000-0xa0000000 503M RW NX SHD > > CONFIG_DEBUG_RODATA=y > CONFIG_DEBUG_ALIGN_RODATA=y > > ---[ Kernel Mapping ]--- > 0x80000000-0x80100000 1M RW NX SHD > 0x80100000-0x80700000 6M ro x SHD > 0x80700000-0x80a00000 3M ro NX SHD > 0x80a00000-0xa0000000 502M RW NX SHD > > CONFIG_DEBUG_RODATA=y > # CONFIG_DEBUG_ALIGN_RODATA is not set > > ---[ Kernel Mapping ]--- > 0x80000000-0x80100000 1M RW NX SHD > 0x80100000-0x80a00000 9M ro x SHD > 0x80a00000-0xa0000000 502M RW NX SHD > > Signed-off-by: Kees Cook <keescook@...omium.org> > --- Reviewed-by: Laura Abbott <labbott@...oraproject.org>
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