This adds a second-stage routine to the usercopy functions that contains the final calculation for the return value, which represents the number of bytes not copied and is returned to the faulting syscall. This is only reached in the code path where a fault occurs during the second in-order copy; otherwise, the intermediate fixup will fall back to returning zero if it reaches the end of the buffer.
As the intermediate fixup has already placed either srcend or dstend in x5 depending on the instruction that faulted, the sub operation is the same and the final fixup can be re-used for both cases. Signed-off-by: Oliver Swede <[email protected]> --- arch/arm64/lib/copy_user_fixup.S | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/arch/arm64/lib/copy_user_fixup.S b/arch/arm64/lib/copy_user_fixup.S index 6a7b2406d948..4858edd55994 100644 --- a/arch/arm64/lib/copy_user_fixup.S +++ b/arch/arm64/lib/copy_user_fixup.S @@ -62,8 +62,17 @@ L(all_copied): mov x0, #0 // reached the end of buffer ret -9998: -// TODO: add accurate fixup L(none_copied): mov x0, x2 // count (x2) ret + +/* + * Faults during a scan of the user buffer while running an + * in-order copy. + * + * Calculate the number of bytes not copied, using the fault + * address as a precise indicator. + */ +9998: + sub x0, x5, addr // x0: srcend-faddr or dstend-faddr + ret -- 2.17.1
