In powerpc pseries system, below behaviour is observed while
enabling tracing on hcall:
# cd /sys/kernel/debug/tracing/
# cat events/powerpc/hcall_exit/enable
0
# echo 1 > events/powerpc/hcall_exit/enable
# ls
-bash: fork: Bad address
Above is from power9 lpar with latest kernel. Past this, softlockup
is observed. Initially while attempting via perf_event_open to
use "PERF_TYPE_TRACEPOINT", kernel panic was observed.
perf config used:
memset([1],0,sizeof(struct perf_event_attr));
pe[1].type=PERF_TYPE_TRACEPOINT;
pe[1].size=96;
pe[1].config=0x26ULL; /* 38 raw_syscalls/sys_exit */
pe[1].sample_type=0; /* 0 */
pe[1].read_format=PERF_FORMAT_TOTAL_TIME_ENABLED|PERF_FORMAT_TOTAL_TIME_RUNNING|PERF_FORMAT_ID|PERF_FORMAT_GROUP|0x10ULL;
/* 1f */
pe[1].inherit=1;
pe[1].precise_ip=0; /* arbitrary skid */
pe[1].wakeup_events=0;
pe[1].bp_type=HW_BREAKPOINT_EMPTY;
pe[1].config1=0x1ULL;
Kernel panic logs:
==
Kernel attempted to read user page (8) - exploit attempt? (uid: 0)
BUG: Kernel NULL pointer dereference on read at 0x0008
Faulting instruction address: 0xc04c2814
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
Modules linked in: nfnetlink bonding tls rfkill sunrpc dm_service_time
dm_multipath pseries_rng xts vmx_crypto xfs libcrc32c sd_mod t10_pi
crc64_rocksoft crc64 sg ibmvfc scsi_transport_fc ibmveth dm_mirror
dm_region_hash dm_log dm_mod fuse
CPU: 0 PID: 1431 Comm: login Not tainted 6.4.0+ #1
Hardware name: IBM,8375-42A POWER9 (raw) 0x4e0202 0xf05
of:IBM,FW950.30 (VL950_892) hv:phyp pSeries
NIP [c04c2814] page_remove_rmap+0x44/0x320
LR [c049c2a4] wp_page_copy+0x384/0xec0
Call Trace:
[c98c7ad0] [c0001416e400] 0xc0001416e400 (unreliable)
[c98c7b20] [c049c2a4] wp_page_copy+0x384/0xec0
[c98c7bf0] [c04a4f64] __handle_mm_fault+0x9d4/0xfb0
[c98c7cf0] [c04a5630] handle_mm_fault+0xf0/0x350
[c98c7d40] [c0094e8c] ___do_page_fault+0x48c/0xc90
[c98c7df0] [c00958a0] hash__do_page_fault+0x30/0x70
[c98c7e20] [c009e244] do_hash_fault+0x1a4/0x330
[c98c7e50] [c0008918]
data_access_common_virt+0x198/0x1f0
--- interrupt: 300 at 0x7fffae971abc
git bisect tracked this down to below commit:
'commit baa49d81a94b ("powerpc/pseries: hvcall stack frame overhead")'
This commit changed STACK_FRAME_OVERHEAD (112 ) to
STACK_FRAME_MIN_SIZE (32 ) since 32 bytes is the minimum size
for ELFv2 stack. With the latest kernel, when running on ELFv2,
STACK_FRAME_MIN_SIZE is used to allocate stack size.
During plpar_hcall_trace, first call is made to HCALL_INST_PRECALL
which saves the registers and allocates new stack frame. In the
plpar_hcall_trace code, STK_PARAM is accessed at two places.
1. To save r4: std r4,STK_PARAM(R4)(r1)
2. To access r4 back: ld r12,STK_PARAM(R4)(r1)
HCALL_INST_PRECALL precall allocates a new stack frame. So all
the stack parameter access after the precall, needs to be accessed
with +STACK_FRAME_MIN_SIZE. So the store instruction should be:
std r4,STACK_FRAME_MIN_SIZE+STK_PARAM(R4)(r1)
If the "std" is not updated with STACK_FRAME_MIN_SIZE, we will
end up with overwriting stack contents and cause corruption.
But instead of updating 'std', we can instead remove it since
HCALL_INST_PRECALL already saves it to the correct location.
similarly load instruction should be:
ld r12,STACK_FRAME_MIN_SIZE+STK_PARAM(R4)(r1)
Fix the load instruction to correctly access the stack parameter
with +STACK_FRAME_MIN_SIZE and remove the store of r4 since the
precall saves it correctly.
Cc: sta...@vger.kernel.org
Fixes: baa49d81a94b ("powerpc/pseries: hvcall stack frame overhead")
Co-developed-by: Naveen N Rao
Signed-off-by: Naveen N Rao
Signed-off-by: Athira Rajeev
---
arch/powerpc/platforms/pseries/hvCall.S | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/hvCall.S
b/arch/powerpc/platforms/pseries/hvCall.S
index bae45b358a09..2addf2ea03f0 100644
--- a/arch/powerpc/platforms/pseries/hvCall.S
+++ b/arch/powerpc/platforms/pseries/hvCall.S
@@ -184,7 +184,6 @@ _GLOBAL_TOC(plpar_hcall)
plpar_hcall_trace:
HCALL_INST_PRECALL(R5)
- std r4,STK_PARAM(R4)(r1)
mr r0,r4
mr r4,r5
@@ -196,7 +195,7 @@ plpar_hcall_trace:
HVSC
- ld r12,STK_PARAM(R4)(r1)
+ ld r12,STACK_FRAME_MIN_SIZE+STK_PARAM(R4)(r1)
std r4,0(r12)
std r5,8(r12)
std r6,16(r12)
@@ -296,7 +295,6 @@ _GLOBAL_TOC(plpar_hcall9)
