[PATCH 5.11 393/775] powerpc/sstep: Fix incorrect return from analyze_instr()

[Greg Kroah-Hartman]

From: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxxxxx>

[ Upstream commit 718aae916fa6619c57c348beaedd675835cf1aa1 ]

We currently just percolate the return value from analyze_instr()
to the caller of emulate_step(), especially if it is a -1.

For one particular case (opcode = 4) for instructions that aren't
currently emulated, we are returning 'should not be single-stepped'
while we should have returned 0 which says 'did not emulate, may
have to single-step'.

Fixes: 930d6288a26787 ("powerpc: sstep: Add support for maddhd, maddhdu, maddld instructions")
Signed-off-by: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxxxxx>
Suggested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Tested-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Sandipan Das <sandipan@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/161157999039.64773.14950289716779364766.stgit@thinktux.local
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/powerpc/lib/sstep.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 5e725ed24d772..33935869e4976 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1447,6 +1447,11 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 
 #ifdef __powerpc64__
 	case 4:
+		/*
+		 * There are very many instructions with this primary opcode
+		 * introduced in the ISA as early as v2.03. However, the ones
+		 * we currently emulate were all introduced with ISA 3.0
+		 */
 		if (!cpu_has_feature(CPU_FTR_ARCH_300))
 			goto unknown_opcode;
 
@@ -1474,7 +1479,7 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 		 * There are other instructions from ISA 3.0 with the same
 		 * primary opcode which do not have emulation support yet.
 		 */
-		return -1;
+		goto unknown_opcode;
 #endif
 
 	case 7:		/* mulli */
-- 
2.27.0