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Subject[PATCH 2/3] powerpc/sstep: Fix kernel crash if VSX is not present
Date
emulate_step() is not checking runtime VSX feature flag before
emulating an instruction. This is causing kernel crash when kernel
is compiled with CONFIG_VSX=y but running on a machine where VSX
is not supported or disabled. Ex, while running emulate_step tests
on P6 machine:

Oops: Exception in kernel mode, sig: 4 [#1]
NIP [c000000000095c24] .load_vsrn+0x28/0x54
LR [c000000000094bdc] .emulate_loadstore+0x167c/0x17b0
Call Trace:
0x40fe240c7ae147ae (unreliable)
.emulate_loadstore+0x167c/0x17b0
.emulate_step+0x25c/0x5bc
.test_lxvd2x_stxvd2x+0x64/0x154
.test_emulate_step+0x38/0x4c
.do_one_initcall+0x5c/0x2c0
.kernel_init_freeable+0x314/0x4cc
.kernel_init+0x24/0x160
.ret_from_kernel_thread+0x58/0xb4

With fix:
emulate_step_test: lxvd2x : FAIL
emulate_step_test: stxvd2x : FAIL

Fixes: https://github.com/linuxppc/linux/issues/148

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
---
arch/powerpc/lib/sstep.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index db6bba259d91..23b7ddf04521 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -2544,6 +2544,15 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
#endif /* __powerpc64__ */

}
+
+#ifdef CONFIG_VSX
+ if ((GETTYPE(op->type) == LOAD_VSX ||
+ GETTYPE(op->type) == STORE_VSX) &&
+ !cpu_has_feature(CPU_FTR_VSX)) {
+ return -1;
+ }
+#endif /* CONFIG_VSX */
+
return 0;

logical_done:
--
2.16.2
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