The __clear_user function is defined to return the number of bytes that could not be cleared. From the underlying memset / bzero implementation this means setting register a2 to that number on return. Currently if a page fault is triggered within the memset_partial block, the value loaded into a2 on return is meaningless.
The label .Lpartial_fixup@ is jumped to on page fault. In order to work out how many bytes failed to copy, the exception handler should find how many bytes left in the partial block (andi a2, STORMASK), add that to the partial block end address (a2), and subtract the faulting address to get the remainder. Currently it incorrectly subtracts the partial block start address (t1), which has additionally has been clobbered to generate a jump target in memset_partial. Fix this by adding the block end address instead.
This issue was found with the following test code: int j, k; for (j = 0; j < 512; j++) { if ((k = clear_user(NULL, j)) != j) { pr_err("clear_user (NULL %d) returned %d\n", j, k); } } Which now passes on Creator Ci40 (MIPS32) and Cavium Octeon II (MIPS64).
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Suggested-by: James Hogan jhogan@kernel.org Signed-off-by: Matt Redfearn matt.redfearn@mips.com
---
Changes in v3: - Just fix the issue at hand
Changes in v2: - Use James Hogan's suggestion of replacing t1 with a0 to get the correct remainder count.
arch/mips/lib/memset.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 90bcdf1224ee..184819c1d5c8 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -252,7 +252,7 @@ PTR_L t0, TI_TASK($28) andi a2, STORMASK LONG_L t0, THREAD_BUADDR(t0) - LONG_ADDU a2, t1 + LONG_ADDU a2, a0 jr ra LONG_SUBU a2, t0