[PATCH 1/3] MIPS: memset.S: Fix clobber of v1 in last_fixup

[PATCH 1/3] MIPS: memset.S: Fix clobber of v1 in last_fixup

[Matt Redfearn]

The label .Llast_fixup\@ is jumped to on page fault within the final
byte set loop of memset (on < MIPSR6 architectures). For some reason, in
this fault handler, the v1 register is randomly set to a2 & STORMASK.
This clobbers v1 for the calling function. This can be observed with the
following test code:

static int __init __attribute__((optimize("O0"))) test_clear_user(void)
{
  register int t asm("v1");
  char *test;
  int j, k;

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

  for (j = 256; j < 512; j++) {
    t = 0xa5a5a5a5;
    if ((k = clear_user(test + PAGE_SIZE - 256, j)) != j - 256) {
        pr_err("clear_user (%px %d) returned %d\n", test + PAGE_SIZE - 256, j, k);
    }
    if (t != 0xa5a5a5a5) {
       pr_err("v1 was clobbered to 0x%x!\n", t);
    }
  }

  return 0;
}
late_initcall(test_clear_user);

Which demonstrates that v1 is indeed clobbered (MIPS64):

Testing clear_user
v1 was clobbered to 0x1!
v1 was clobbered to 0x2!
v1 was clobbered to 0x3!
v1 was clobbered to 0x4!
v1 was clobbered to 0x5!
v1 was clobbered to 0x6!
v1 was clobbered to 0x7!

Since the number of bytes that could not be set is already contained in
a2, the andi placing a value in v1 is not necessary and actively
harmful in clobbering v1.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: James Hogan <jhogan@kernel.org>
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
---

 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 fa3bec269331..84e91f4fdf53 100644
--- a/arch/mips/lib/memset.S
+++ b/arch/mips/lib/memset.S
@@ -258,7 +258,7 @@
 
 .Llast_fixup\@:
 	jr		ra
-	andi		v1, a2, STORMASK
+	 nop
 
 .Lsmall_fixup\@:
 	PTR_SUBU	a2, t1, a0
-- 
2.7.4

[PATCH 2/3] MIPS: uaccess: Add micromips clobbers to bzero invocation

[Matt Redfearn]

The micromips implementation of bzero additionally clobbers registers t7
& t8. Specify this in the clobbers list when invoking bzero.

Reported-by: James Hogan <jhogan@kernel.org>
Fixes: 26c5e07d1478 ("MIPS: microMIPS: Optimise 'memset' core library function.")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
---

 arch/mips/include/asm/uaccess.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index b71306947290..06629011a434 100644
--- a/arch/mips/include/asm/uaccess.h
+++ b/arch/mips/include/asm/uaccess.h
@@ -654,6 +654,13 @@ __clear_user(void __user *addr, __kernel_size_t size)
 {
 	__kernel_size_t res;
 
+#ifdef CONFIG_CPU_MICROMIPS
+/* micromips memset / bzero also clobbers t7 & t8 */
+#define bzero_clobbers "$4", "$5", "$6", __UA_t0, __UA_t1, "$15", "$24", "$31"
+#else
+#define bzero_clobbers "$4", "$5", "$6", __UA_t0, __UA_t1, "$31"
+#endif /* CONFIG_CPU_MICROMIPS */
+
 	if (eva_kernel_access()) {
 		__asm__ __volatile__(
 			"move\t$4, %1\n\t"
@@ -663,7 +670,7 @@ __clear_user(void __user *addr, __kernel_size_t size)
 			"move\t%0, $6"
 			: "=r" (res)
 			: "r" (addr), "r" (size)
-			: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
+			: bzero_clobbers);
 	} else {
 		might_fault();
 		__asm__ __volatile__(
@@ -674,7 +681,7 @@ __clear_user(void __user *addr, __kernel_size_t size)
 			"move\t%0, $6"
 			: "=r" (res)
 			: "r" (addr), "r" (size)
-			: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
+			: bzero_clobbers);
 	}
 
 	return res;
-- 
2.7.4

[PATCH 3/3] MIPS: memset.S: Reinstate delay slot indentation

[Matt Redfearn]

Assembly language within the MIPS kernel conventionally indents
instructions which are in a branch delay slot to make them easier to
see. Commit 8483b14aaa81 ("MIPS: lib: memset: Whitespace fixes") rather
inexplicably removed all of these indentations from memset.S. Reinstate
the convention for all instructions in a branch delay slot. This
effectively reverts the above commit, plus other locations introduced
with MIPSR6 support.

Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
---

 arch/mips/lib/memset.S | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S
index 84e91f4fdf53..085cc86f624f 100644
--- a/arch/mips/lib/memset.S
+++ b/arch/mips/lib/memset.S
@@ -95,7 +95,7 @@
 
 	sltiu		t0, a2, STORSIZE	/* very small region? */
 	bnez		t0, .Lsmall_memset\@
-	andi		t0, a0, STORMASK	/* aligned? */
+	 andi		t0, a0, STORMASK	/* aligned? */
 
 #ifdef CONFIG_CPU_MICROMIPS
 	move		t8, a1			/* used by 'swp' instruction */
@@ -103,12 +103,12 @@
 #endif
 #ifndef CONFIG_CPU_DADDI_WORKAROUNDS
 	beqz		t0, 1f
-	PTR_SUBU	t0, STORSIZE		/* alignment in bytes */
+	 PTR_SUBU	t0, STORSIZE		/* alignment in bytes */
 #else
 	.set		noat
 	li		AT, STORSIZE
 	beqz		t0, 1f
-	PTR_SUBU	t0, AT			/* alignment in bytes */
+	 PTR_SUBU	t0, AT			/* alignment in bytes */
 	.set		at
 #endif
 
@@ -149,7 +149,7 @@
 1:	ori		t1, a2, 0x3f		/* # of full blocks */
 	xori		t1, 0x3f
 	beqz		t1, .Lmemset_partial\@	/* no block to fill */
-	andi		t0, a2, 0x40-STORSIZE
+	 andi		t0, a2, 0x40-STORSIZE
 
 	PTR_ADDU	t1, a0			/* end address */
 	.set		reorder
@@ -174,7 +174,7 @@
 	.set		at
 #endif
 	jr		t1
-	PTR_ADDU	a0, t0			/* dest ptr */
+	 PTR_ADDU	a0, t0			/* dest ptr */
 
 	.set		push
 	.set		noreorder
@@ -186,7 +186,7 @@
 
 	beqz		a2, 1f
 #ifndef CONFIG_CPU_MIPSR6
-	PTR_ADDU	a0, a2			/* What's left */
+	 PTR_ADDU	a0, a2			/* What's left */
 	R10KCBARRIER(0(ra))
 #ifdef __MIPSEB__
 	EX(LONG_S_R, a1, -1(a0), .Llast_fixup\@)
@@ -194,7 +194,7 @@
 	EX(LONG_S_L, a1, -1(a0), .Llast_fixup\@)
 #endif
 #else
-	PTR_SUBU	t0, $0, a2
+	 PTR_SUBU	t0, $0, a2
 	PTR_ADDIU	t0, 1
 	STORE_BYTE(0)
 	STORE_BYTE(1)
@@ -210,11 +210,11 @@
 0:
 #endif
 1:	jr		ra
-	move		a2, zero
+	 move		a2, zero
 
 .Lsmall_memset\@:
 	beqz		a2, 2f
-	PTR_ADDU	t1, a0, a2
+	 PTR_ADDU	t1, a0, a2
 
 1:	PTR_ADDIU	a0, 1			/* fill bytewise */
 	R10KCBARRIER(0(ra))
@@ -222,7 +222,7 @@
 	 EX(sb, a1, -1(a0), .Lsmall_fixup\@)
 
 2:	jr		ra			/* done */
-	move		a2, zero
+	 move		a2, zero
 	.if __memset == 1
 	END(memset)
 	.set __memset, 0
@@ -238,7 +238,7 @@
 
 .Lfirst_fixup\@:
 	jr	ra
-	nop
+	 nop
 
 .Lfwd_fixup\@:
 	PTR_L		t0, TI_TASK($28)
@@ -246,7 +246,7 @@
 	LONG_L		t0, THREAD_BUADDR(t0)
 	LONG_ADDU	a2, t1
 	jr		ra
-	LONG_SUBU	a2, t0
+	 LONG_SUBU	a2, t0
 
 .Lpartial_fixup\@:
 	PTR_L		t0, TI_TASK($28)
@@ -278,7 +278,7 @@
 LEAF(memset)
 EXPORT_SYMBOL(memset)
 	beqz		a1, 1f
-	move		v0, a0			/* result */
+	 move		v0, a0			/* result */
 
 	andi		a1, 0xff		/* spread fillword */
 	LONG_SLL		t1, a1, 8
-- 
2.7.4