• Will Deacon's avatar
    ARM: 7954/1: mm: remove remaining domain support from ARMv6 · b6ccb980
    Will Deacon authored
    CPU_32v6 currently selects CPU_USE_DOMAINS if CPU_V6 and MMU. This is
    because ARM 1136 r0pX CPUs lack the v6k extensions, and therefore do
    not have hardware thread registers. The lack of these registers requires
    the kernel to update the vectors page at each context switch in order to
    write a new TLS pointer. This write must be done via the userspace
    mapping, since aliasing caches can lead to expensive flushing when using
    kmap. Finally, this requires the vectors page to be mapped r/w for
    kernel and r/o for user, which has implications for things like put_user
    which must trigger CoW appropriately when targetting user pages.
    
    The upshot of all this is that a v6/v7 kernel makes use of domains to
    segregate kernel and user memory accesses. This has the nasty
    side-effect of making device mappings executable, which has been
    observed to cause subtle bugs on recent cores (e.g. Cortex-A15
    performing a speculative instruction fetch from the GIC and acking an
    interrupt in the process).
    
    This patch solves this problem by removing the remaining domain support
    from ARMv6. A new memory type is added specifically for the vectors page
    which allows that page (and only that page) to be mapped as user r/o,
    kernel r/w. All other user r/o pages are mapped also as kernel r/o.
    Patch co-developed with Russell King.
    
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    b6ccb980
proc-macros.S 7.71 KB