• Russell King's avatar
    ARM: software-based priviledged-no-access support · a5e090ac
    Russell King authored
    Provide a software-based implementation of the priviledged no access
    support found in ARMv8.1.
    
    Userspace pages are mapped using a different domain number from the
    kernel and IO mappings.  If we switch the user domain to "no access"
    when we enter the kernel, we can prevent the kernel from touching
    userspace.
    
    However, the kernel needs to be able to access userspace via the
    various user accessor functions.  With the wrapping in the previous
    patch, we can temporarily enable access when the kernel needs user
    access, and re-disable it afterwards.
    
    This allows us to trap non-intended accesses to userspace, eg, caused
    by an inadvertent dereference of the LIST_POISON* values, which, with
    appropriate user mappings setup, can be made to succeed.  This in turn
    can allow use-after-free bugs to be further exploited than would
    otherwise be possible.
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    a5e090ac
swp_emulate.c 7.04 KB