[PATCH 5.11 128/152] powerpc/mm/book3s64: Use the correct storage key value when calling H_PROTECT

Greg Kroah-Hartman
2021-04-05T09:22:10Z

From: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

[ Upstream commit 53f1d31708f6240e4615b0927df31f182e389e2f ]

H_PROTECT expects the flag value to include flags:
AVPN, pp0, pp1, pp2, key0-key4, Noexec, CMO Option flags

This patch updates hpte_updatepp() to fetch the storage key value from
the linux page table and use the same in H_PROTECT hcall.

native_hpte_updatepp() is not updated because the kernel doesn't clear
the existing storage key value there. The kernel also doesn't use
hpte_updatepp() callback for updating storage keys.

This fixes the below kernel crash observed with KUAP enabled.

BUG: Unable to handle kernel data access on write at 0xc009fffffc440000
Faulting instruction address: 0xc0000000000b7030
Key fault AMR: 0xfcffffffffffffff IAMR: 0xc0000077bc498100
Found HPTE: v = 0x40070adbb6fffc05 r = 0x1ffffffffff1194
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
...
CFAR: c000000000010100 DAR: c009fffffc440000 DSISR: 02200000 IRQMASK: 0
...
NIP memset+0x68/0x104
LR pcpu_alloc+0x54c/0xb50
Call Trace:
pcpu_alloc+0x55c/0xb50 (unreliable)
blk_stat_alloc_callback+0x94/0x150
blk_mq_init_allocated_queue+0x64/0x560
blk_mq_init_queue+0x54/0xb0
scsi_mq_alloc_queue+0x30/0xa0
scsi_alloc_sdev+0x1cc/0x300
scsi_probe_and_add_lun+0xb50/0x1020
__scsi_scan_target+0x17c/0x790
scsi_scan_channel+0x90/0xe0
scsi_scan_host_selected+0x148/0x1f0
do_scan_async+0x2c/0x2a0
async_run_entry_fn+0x78/0x220
process_one_work+0x264/0x540
worker_thread+0xa8/0x600
kthread+0x190/0x1a0
ret_from_kernel_thread+0x5c/0x6c

With KUAP enabled the kernel uses storage key 3 for all its
translations. But as shown by the debug print, in this specific case we
have the hash page table entry created with key value 0.

Found HPTE: v = 0x40070adbb6fffc05 r = 0x1ffffffffff1194

and DSISR indicates a key fault.

This can happen due to parallel fault on the same EA by different CPUs:

CPU 0 CPU 1
fault on X

H_PAGE_BUSY set
fault on X

finish fault handling and
clear H_PAGE_BUSY
check for H_PAGE_BUSY
continue with fault handling.

This implies CPU1 will end up calling hpte_updatepp for address X and
the kernel updated the hash pte entry with key 0

Fixes: d94b827e89dc ("powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation")
Reported-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Debugged-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210326070755.304625-1-aneesh.kumar@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/platforms/pseries/lpar.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 764170fdb0f7..3805519a6469 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -887,7 +887,8 @@ static long pSeries_lpar_hpte_updatepp(unsigned long slot,

want_v = hpte_encode_avpn(vpn, psize, ssize);

- flags = (newpp & 7) | H_AVPN;
+ flags = (newpp & (HPTE_R_PP | HPTE_R_N | HPTE_R_KEY_LO)) | H_AVPN;
+ flags |= (newpp & HPTE_R_KEY_HI) >> 48;
if (mmu_has_feature(MMU_FTR_KERNEL_RO))
/* Move pp0 into bit 8 (IBM 55) */
flags |= (newpp & HPTE_R_PP0) >> 55;
--
2.30.2