• Dave Martin's avatar
    arm64: uaccess: Fix omissions from usercopy whitelist · 65896545
    Dave Martin authored
    When the hardend usercopy support was added for arm64, it was
    concluded that all cases of usercopy into and out of thread_struct
    were statically sized and so didn't require explicit whitelisting
    of the appropriate fields in thread_struct.
    
    Testing with usercopy hardening enabled has revealed that this is
    not the case for certain ptrace regset manipulation calls on arm64.
    This occurs because the sizes of usercopies associated with the
    regset API are dynamic by construction, and because arm64 does not
    always stage such copies via the stack: indeed the regset API is
    designed to avoid the need for that by adding some bounds checking.
    
    This is currently believed to affect only the fpsimd and TLS
    registers.
    
    Because the whitelisted fields in thread_struct must be contiguous,
    this patch groups them together in a nested struct.  It is also
    necessary to be able to determine the location and size of that
    struct, so rather than making the struct anonymous (which would
    save on edits elsewhere) or adding an anonymous union containing
    named and unnamed instances of the same struct (gross), this patch
    gives the struct a name and makes the necessary edits to code that
    references it (noisy but simple).
    
    Care is needed to ensure that the new struct does not contain
    padding (which the usercopy hardening would fail to protect).
    
    For this reason, the presence of tp2_value is made unconditional,
    since a padding field would be needed there in any case.  This pads
    up to the 16-byte alignment required by struct user_fpsimd_state.
    Acked-by: default avatarKees Cook <keescook@chromium.org>
    Reported-by: default avatarMark Rutland <mark.rutland@arm.com>
    Fixes: 9e8084d3 ("arm64: Implement thread_struct whitelist for hardened usercopy")
    Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    65896545
sys_compat.c 3.32 KB