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Date: Wed, 4 Nov 2015 17:13:59 -0800 From: Kees Cook <keescook@...omium.org> To: Laura Abbott <labbott@...oraproject.org> Cc: Russell King <linux@....linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org> Subject: Re: [PATCH] arm: Use kernel mm when updating section permissions On Wed, Nov 4, 2015 at 5:06 PM, Kees Cook <keescook@...omium.org> wrote: > On Wed, Nov 4, 2015 at 5:00 PM, Laura Abbott <labbott@...oraproject.org> wrote: >> Currently, read only permissions are not being applied even >> when CONFIG_DEBUG_RODATA is set. This is because section_update >> uses current->mm for adjusting the page tables. current->mm >> need not be equivalent to the kernel version. Use pgd_offset_k >> to get the proper page directory for updating. >> >> Signed-off-by: Laura Abbott <labbott@...oraproject.org> >> --- >> I found this while trying to convince myself of something. >> Dumping the page table via debugfs and writing to kernel text were both >> showing the lack of mappings. This was observed on QEMU. Maybe it's just a >> QEMUism but if not it probably should go to stable. > > Well that's weird! debugfs showed the actual permissions that lacked > RO? I wonder what changed. I tested this both with debugfs and lkdtm's > KERN_WRITE test when the patches originally landed. The comment will need adjusting too. I have a memory of needing to use current->mm to deal with some crazy errata and handling TLB flushes... -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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