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ARM: 8721/1: mm: dump: check hardware RO bit for LPAE 

When CONFIG_ARM_LPAE is set, the PMD dump relies on the software
read-only bit to determine whether a page is writable. This
concealed a bug which left the kernel text section writable
(AP2=0) while marked read-only in the software bit.

In a kernel with the AP2 bug, the dump looks like this:

    ---[ Kernel Mapping ]---
    0xc0000000-0xc0200000           2M RW NX SHD
    0xc0200000-0xc0600000           4M ro x  SHD
    0xc0600000-0xc0800000           2M ro NX SHD
    0xc0800000-0xc4800000          64M RW NX SHD

The fix is to check that the software and hardware bits are both
set before displaying "ro". The dump then shows the true perms:

    ---[ Kernel Mapping ]---
    0xc0000000-0xc0200000           2M RW NX SHD
    0xc0200000-0xc0600000           4M RW x  SHD
    0xc0600000-0xc0800000           2M RW NX SHD
    0xc0800000-0xc4800000          64M RW NX SHD

Fixes: ded9477984 ("ARM: 8109/1: mm: Modify pte_write and pmd_write logic for LPAE")
Signed-off-by: Philip Derrin <philip@cog.systems>
Tested-by: Neil Dick <neil@cog.systems>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Philip Derrin 2017-11-14 00:55:26 +01:00 committed by Russell King
parent 29337b60ab
commit 3b0c0c922f
1 changed files with 2 additions and 2 deletions
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4
arch/arm/mm/dump.c
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@ -129,8 +129,8 @@ static const struct prot_bits section_bits[] = {
.val = PMD_SECT_USER,
.set = "USR",
}, {
.mask = L_PMD_SECT_RDONLY,
.val = L_PMD_SECT_RDONLY,
.mask = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
.val = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
.set = "ro",
.clear = "RW",
#elif __LINUX_ARM_ARCH__ >= 6