The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b1c03f1ef48d36ff28afb06e8f0c1233ef072f1d Mon Sep 17 00:00:00 2001

From: Matt Redfearn matt.redfearn@mips.com Date: Wed, 23 May 2018 14:39:58 +0100 Subject: [PATCH] MIPS: memset.S: Fix byte_fixup for MIPSr6

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 MIPSr6 version of setting of initial unaligned bytes, the value loaded into a2 on return is meaningless.

During the MIPSr6 version of the initial unaligned bytes block, register a2 contains the number of bytes to be set beyond the initial unaligned bytes. The t0 register is initally set to the number of unaligned bytes - STORSIZE, effectively a negative version of the number of unaligned bytes. This is then incremented before each byte is saved.

The label .Lbyte_fixup@ is jumped to on page fault. Currently the value in a2 is incorrectly replaced by 0 - t0 + 1, effectively the number of unaligned bytes remaining. This leads to the failures being reported by the following test code:

static int __init test_clear_user(void) { int j, k;

pr_info("\n\n\nTesting clear_user\n"); for (j = 0; j < 512; j++) { if ((k = clear_user(NULL+3, j)) != j) { pr_err("clear_user (NULL %d) returned %d\n", j, k); } } return 0; } late_initcall(test_clear_user);

Which reports: [ 3.965439] Testing clear_user [ 3.973169] clear_user (NULL 8) returned 6 [ 3.976782] clear_user (NULL 9) returned 6 [ 3.980390] clear_user (NULL 10) returned 6 [ 3.984052] clear_user (NULL 11) returned 6 [ 3.987524] clear_user (NULL 12) returned 6

Fix this by subtracting t0 from a2 (rather than $0), effectivey giving: unset_bytes = (#bytes - (#unaligned bytes)) - (-#unaligned bytes remaining + 1) + 1 a2 = a2 - t0 + 1

This fixes the value returned from __clear user when the number of bytes to set is > LONGSIZE and the address is invalid and unaligned.

Unfortunately, this breaks the fixup handling for unaligned bytes after the final long, where register a2 still contains the number of bytes remaining to be set and the t0 register is to 0 - the number of unaligned bytes remaining.

Because t0 is now is now subtracted from a2 rather than 0, the number of bytes unset is reported incorrectly:

static int __init test_clear_user(void) { char *test; int j, k;

pr_info("\n\n\nTesting clear_user\n"); test = vmalloc(PAGE_SIZE);

for (j = 256; j < 512; j++) { if ((k = clear_user(test + PAGE_SIZE - 254, j)) != j - 254) { pr_err("clear_user (%px %d) returned %d\n", test + PAGE_SIZE - 254, j, k); } } return 0; } late_initcall(test_clear_user);

[ 3.976775] clear_user (c00000000000df02 256) returned 4 [ 3.981957] clear_user (c00000000000df02 257) returned 6 [ 3.986425] clear_user (c00000000000df02 258) returned 8 [ 3.990850] clear_user (c00000000000df02 259) returned 10 [ 3.995332] clear_user (c00000000000df02 260) returned 12 [ 3.999815] clear_user (c00000000000df02 261) returned 14

Fix this by ensuring that a2 is set to 0 during the set of final unaligned bytes.

Signed-off-by: Matt Redfearn matt.redfearn@mips.com Signed-off-by: Paul Burton paul.burton@mips.com Fixes: 8c56208aff77 ("MIPS: lib: memset: Add MIPS R6 support") Patchwork: https://patchwork.linux-mips.org/patch/19338/ Cc: James Hogan jhogan@kernel.org Cc: Ralf Baechle ralf@linux-mips.org Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v4.0+

diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 1cc306520a55..fac26ce64b2f 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -195,6 +195,7 @@ #endif #else PTR_SUBU t0, $0, a2 + move a2, zero /* No remaining longs */ PTR_ADDIU t0, 1 STORE_BYTE(0) STORE_BYTE(1) @@ -231,7 +232,7 @@

#ifdef CONFIG_CPU_MIPSR6 .Lbyte_fixup@: - PTR_SUBU a2, $0, t0 + PTR_SUBU a2, t0 jr ra PTR_ADDIU a2, 1 #endif /* CONFIG_CPU_MIPSR6 */