Re: [PATCH v3 0/6] ARM: mm: cleanup page fault and fix pxn process issue

From: Kefeng Wang
Date: Mon Jun 14 2021 - 22:35:01 EST

On 2021/6/10 20:35, Kefeng Wang wrote:
The patchset cleanup ARM page fault handle to improve readability,
fix the page table entries printing and fix infinite loop in the
page fault handler when user code execution with privilege mode if
ARM_LPAE enabled.

echo EXEC_USERSPACE > /sys/kernel/debug/provoke-crash/DIRECT

lkdtm: Performing direct entry EXEC_USERSPACE
lkdtm: attempting ok execution at c0717674
lkdtm: attempting bad execution at b6fd6000
rcu: INFO: rcu_sched self-detected stall on CPU
rcu: 1-....: (2100 ticks this GP) idle=7e2/1/0x40000002 softirq=136/136 fqs=1050
(t=2101 jiffies g=-1027 q=16)
NMI backtrace for cpu 1
CPU: 1 PID: 57 Comm: sh Not tainted 5.13.0-rc4 #126
r9:c1f04000 r8:c0e04cc8 r7:c1f05cbc r6:ffffffff r5:60000113 r4:c03724f8
[<c03722e0>] (handle_mm_fault) from [<c02152f4>] (do_page_fault+0x1a0/0x3d8)
r10:c180ec48 r9:c11b1aa0 r8:c11b1ac0 r7:8000020f r6:b6fd6000 r5:c180ec00
[<c0215154>] (do_page_fault) from [<c02157cc>] (do_PrefetchAbort+0x40/0x94)
r10:0000000f r9:c1f04000 r8:c1f05df8 r7:b6fd6000 r6:c0215154 r5:0000020f
[<c021578c>] (do_PrefetchAbort) from [<c0200c50>] (__pabt_svc+0x50/0x80)
Exception stack(0xc1f05df8 to 0xc1f05e40)
5de0: 0000002b 2e34f000
5e00: 3ee77213 3ee77213 b6fd6000 c0b51020 c140d000 c0a4b5dc 0000000f c1f05f58
5e20: 0000000f c1f05e64 c1f05d88 c1f05e48 c0717a6c b6fd6000 60000013 ffffffff
r8:0000000f r7:c1f05e2c r6:ffffffff r5:60000013 r4:b6fd6000
[<c07179a8>] (lkdtm_EXEC_USERSPACE) from [<c09a51b8>] (lkdtm_do_action+0x48/0x4c)

lkdtm: Performing direct entry EXEC_USERSPACE
lkdtm: attempting ok execution at c07176d4
lkdtm: attempting bad execution at b6f57000
8<--- cut here ---
Unable to handle kernel execution of memory at virtual address b6f57000
pgd = 81e20f00
[b6f57000] *pgd=81e23003, *pmd=13ee9c003
Internal error: Oops: 8000020f [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 57 Comm: sh Not tainted 5.13.0-rc4+ #127
Hardware name: ARM-Versatile Express
PC is at 0xb6f57000
LR is at lkdtm_EXEC_USERSPACE+0xc4/0xd4
pc : [<b6f57000>] lr : [<c0717acc>] psr: 60000013
sp : c1f3de48 ip : c1f3dd88 fp : c1f3de64
r10: 0000000f r9 : c1f3df58 r8 : 0000000f
r7 : c0a4b5dc r6 : c1f1d000 r5 : c0b51070 r4 :b6f57000
r3 : 7e62f7da r2 : 7e62f7da r1 : 2e330000 r0 :0000002b
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user

Hi Russell, I fix patches according your comment.

Especially the patch 6,any new suggest about it, thanks.

- drop the fix about page table printing
- kill page table base print instead of printing the physical address
- only die when permission fault both kernel-mode and user code execution
with privilege mode
- drop LPAE specific

- split patch into smaller changes suggested by Russell
- fix page table printing in show_pte()
- add new die_kernel_fault() helper
- report "execution of user memory" when user code execution with
privilege mode

Kefeng Wang (6):
ARM: mm: Rafactor the __do_page_fault()
ARM: mm: Kill task_struct argument for __do_page_fault()
ARM: mm: Cleanup access_error()
ARM: mm: Kill page table base print in show_pte()
ARM: mm: Provide die_kernel_fault() helper
ARM: mm: Fix PXN process with LPAE feature

arch/arm/mm/fault.c | 119 +++++++++++++++++++++++---------------------
arch/arm/mm/fault.h | 4 ++
2 files changed, 67 insertions(+), 56 deletions(-)