[PATCH 4.9 034/171] MIPS: microMIPS: Fix decoding of swsp16 instruction

Greg Kroah-Hartman
2018-11-08T22:03:52Z

[ Upstream commit cea8cd498f4f1c30ea27e3664b3c671e495c4fce ]

When the immediate encoded in the instruction is accessed, it is sign
extended due to being a signed value being assigned to a signed integer.
The ISA specifies that this operation is an unsigned operation.
The sign extension leads us to incorrectly decode:

801e9c8e: cbf1 sw ra,68(sp)

As having an immediate of 1073741809.

Since the instruction format does not specify signed/unsigned, and this
is currently the only location to use this instuction format, change it
to an unsigned immediate.

Fixes: bb9bc4689b9c ("MIPS: Calculate microMIPS ra properly when unwinding the stack")
Suggested-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: Miodrag Dinic <miodrag.dinic@imgtec.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16957/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/mips/include/uapi/asm/inst.h | 2 +-
arch/mips/kernel/process.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/uapi/asm/inst.h b/arch/mips/include/uapi/asm/inst.h
index 77429d1622b3..711d9b8465b8 100644
--- a/arch/mips/include/uapi/asm/inst.h
+++ b/arch/mips/include/uapi/asm/inst.h
@@ -964,7 +964,7 @@ struct mm16_r3_format { /* Load from global pointer format */
struct mm16_r5_format { /* Load/store from stack pointer format */
__BITFIELD_FIELD(unsigned int opcode : 6,
__BITFIELD_FIELD(unsigned int rt : 5,
- __BITFIELD_FIELD(signed int simmediate : 5,
+ __BITFIELD_FIELD(unsigned int imm : 5,
__BITFIELD_FIELD(unsigned int : 16, /* Ignored */
;))))
};
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index ba315e523b33..0211dc737a21 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -212,7 +212,7 @@ static inline int is_ra_save_ins(union mips_instruction *ip, int *poff)
if (ip->mm16_r5_format.rt != 31)
return 0;

- *poff = ip->mm16_r5_format.simmediate;
+ *poff = ip->mm16_r5_format.imm;
*poff = (*poff << 2) / sizeof(ulong);
return 1;

--
2.17.1