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    Subject[PATCH 4.9 014/138] ARM: 8722/1: mm: make STRICT_KERNEL_RWX effective for LPAE
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Philip Derrin <philip@cog.systems>

    commit 400eeffaffc7232c0ae1134fe04e14ae4fb48d8c upstream.

    Currently, for ARM kernels with CONFIG_ARM_LPAE and
    CONFIG_STRICT_KERNEL_RWX enabled, the 2MiB pages mapping the
    kernel code and rodata are writable. They are marked read-only in
    a software bit (L_PMD_SECT_RDONLY) but the hardware read-only bit
    is not set (PMD_SECT_AP2).

    For user mappings, the logic that propagates the software bit
    to the hardware bit is in set_pmd_at(); but for the kernel,
    section_update() writes the PMDs directly, skipping this logic.

    The fix is to set PMD_SECT_AP2 for read-only sections in
    section_update(), at the same time as L_PMD_SECT_RDONLY.

    Fixes: 1e3479225acb ("ARM: 8275/1: mm: fix PMD_SECT_RDONLY undeclared compile error")
    Signed-off-by: Philip Derrin <philip@cog.systems>
    Reported-by: Neil Dick <neil@cog.systems>
    Tested-by: Neil Dick <neil@cog.systems>
    Tested-by: Laura Abbott <labbott@redhat.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/mm/init.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/arch/arm/mm/init.c
    +++ b/arch/arm/mm/init.c
    @@ -619,8 +619,8 @@ static struct section_perm ro_perms[] =
    .start = (unsigned long)_stext,
    .end = (unsigned long)__init_begin,
    #ifdef CONFIG_ARM_LPAE
    - .mask = ~L_PMD_SECT_RDONLY,
    - .prot = L_PMD_SECT_RDONLY,
    + .mask = ~(L_PMD_SECT_RDONLY | PMD_SECT_AP2),
    + .prot = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
    #else
    .mask = ~(PMD_SECT_APX | PMD_SECT_AP_WRITE),
    .prot = PMD_SECT_APX | PMD_SECT_AP_WRITE,

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