[PATCH] Fix Kernel crash for MIPS rel6 in jump label branch function.

[PATCH] Fix Kernel crash for MIPS rel6 in jump label branch function.

[Archer Yan]

Insert Branch instruction instead of NOP to make sure assembler don't
patch code in forbidden slot. In jump label function, it might
be possible to patch Control Transfer Instructions(CTIs) into
forbidden slot, which will generate Reserved Instruction exception
in MIPS release 6.

Signed-off-by: Archer Yan <ayan@wavecomp.com>
Reviewed-by: Paul Burton <paul.burton@mips.com>
---
 arch/mips/include/asm/jump_label.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/mips/include/asm/jump_label.h b/arch/mips/include/asm/jump_label.h
index e77672539e8e..e4456e450f94 100644
--- a/arch/mips/include/asm/jump_label.h
+++ b/arch/mips/include/asm/jump_label.h
@@ -21,15 +21,15 @@
 #endif
 
 #ifdef CONFIG_CPU_MICROMIPS
-#define NOP_INSN "nop32"
+#define B_INSN "b32"
 #else
-#define NOP_INSN "nop"
+#define B_INSN "b"
 #endif
 
 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
-	asm_volatile_goto("1:\t" NOP_INSN "\n\t"
-		"nop\n\t"
+	asm_volatile_goto("1:\t" B_INSN " 2f\n\t"
+		"2:\tnop\n\t"
 		".pushsection __jump_table,  \"aw\"\n\t"
 		WORD_INSN " 1b, %l[l_yes], %0\n\t"
 		".popsection\n\t"
-- 
2.17.1

Re: [PATCH] Fix Kernel crash for MIPS rel6 in jump label branch function.

[Paul Burton]

Hello,

Archer Yan wrote:
> Insert Branch instruction instead of NOP to make sure assembler don't
> patch code in forbidden slot. In jump label function, it might
> be possible to patch Control Transfer Instructions(CTIs) into
> forbidden slot, which will generate Reserved Instruction exception
> in MIPS release 6.
> 
> Signed-off-by: Archer Yan <ayan@wavecomp.com>
> Reviewed-by: Paul Burton <paul.burton@mips.com>

Applied to mips-fixes.

Thanks,
    Paul

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