From 39b5a4d1e505949796877291322d2e4a74e2e392 Mon Sep 17 00:00:00 2001 From: Reza Arbab Date: Sat, 6 Jul 2019 15:16:47 +0530 Subject: [PATCH] powerpc/64s: save r13 in MCE handler (simulator workaroud) Testing my memcpy_mcsafe() work in progress with an injected UE, I get an error like this immediately after the function returns: BUG: Unable to handle kernel data access at 0x7fff84dec8f8 Faulting instruction address: 0xc0080000009c00b0 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Radix MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV Modules linked in: mce(O+) vmx_crypto crc32c_vpmsum CPU: 0 PID: 1375 Comm: modprobe Tainted: G O 5.1.0-rc6 #267 NIP: c0080000009c00b0 LR: c0080000009c00a8 CTR: c000000000095f90 REGS: c0000000ee197790 TRAP: 0300 Tainted: G O (5.1.0-rc6) MSR: 900000000280b033 CR: 88002826 XER: 00040000 CFAR: c000000000095f8c DAR: 00007fff84dec8f8 DSISR: 40000000 IRQMASK: 0 GPR00: 000000006c6c6568 c0000000ee197a20 c0080000009c8400 fffffffffffffff2 GPR04: c0080000009c02e0 0000000000000006 0000000000000000 c000000003c834c8 GPR08: 0080000000000000 776a6681b7fb5100 0000000000000000 c0080000009c01c8 GPR12: c000000000095f90 00007fff84debc00 000000004d071440 0000000000000000 GPR16: 0000000100000601 c0080000009e0000 c000000000c98dd8 c000000000c98d98 GPR20: c000000003bba970 c0080000009c04d0 c0080000009c0618 c0000000001e5820 GPR24: 0000000000000000 0000000000000100 0000000000000001 c000000003bba958 GPR28: c0080000009c02e8 c0080000009c0318 c0080000009c02e0 0000000000000000 NIP [c0080000009c00b0] cause_ue+0xa8/0xe8 [mce] LR [c0080000009c00a8] cause_ue+0xa0/0xe8 [mce] After debugging we see that the first instruction at vector 200 is skipped by the simulator, due to which r13 is not saved. Adding a nop at 0x200 fixes the issue. (This commit is needed for testing this series. This should not be taken into the tree) --- arch/powerpc/kernel/exceptions-64s.S | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 73ba246ca11d2b..8e43abb2a744e1 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -255,6 +255,7 @@ EXC_REAL_BEGIN(machine_check, 0x200, 0x100) * some code path might still want to branch into the original * vector */ + nop SET_SCRATCH0(r13) /* save r13 */ EXCEPTION_PROLOG_0(PACA_EXMC) BEGIN_FTR_SECTION