Re: [PATCH] ARM: fix panic when kasan and kprobe are enabled

[Shaobo Huang]

On Sat, 17 Jul 2021 at 01:01, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> On Wed, 14 Jul 2021 at 10:27, Shaobo Huang <huangshaobo6@xxxxxxxxxx> wrote:
>>
>> From: huangshaobo <huangshaobo6@xxxxxxxxxx>
>>
>> arm32 uses software to simulate the instruction replaced
>> by kprobe. some instructions may be simulated by constructing
>> assembly functions. therefore, before executing instruction
>> simulation, it is necessary to construct assembly function
>> execution environment in C language through binding registers.
>> after kasan is enabled, the register binding relationship will
>> be destroyed, resulting in instruction simulation errors and
>> causing kernel panic.
>>
>> the kprobe emulate instruction function is distributed in three
>> files: actions-common.c actions-arm.c actions-thumb.c, so disable
>> KASAN when compiling these files.
>>
>> for example, use kprobe insert on cap_capable+20 after kasan
>> enabled, the cap_capable assembly code is as follows:
>> <cap_capable>:
>> e92d47f0        push    {r4, r5, r6, r7, r8, r9, sl, lr}
>> e1a05000        mov     r5, r0
>> e280006c        add     r0, r0, #108    ; 0x6c
>> e1a04001        mov     r4, r1
>> e1a06002        mov     r6, r2
>> e59fa090        ldr     sl, [pc, #144]  ;
>> ebfc7bf8        bl      c03aa4b4 <__asan_load4>
>> e595706c        ldr     r7, [r5, #108]  ; 0x6c
>> e2859014        add     r9, r5, #20
>> ......
>> The emulate_ldr assembly code after enabling kasan is as follows:
>> c06f1384 <emulate_ldr>:
>> e92d47f0        push    {r4, r5, r6, r7, r8, r9, sl, lr}
>> e282803c        add     r8, r2, #60     ; 0x3c
>> e1a05000        mov     r5, r0
>> e7e37855        ubfx    r7, r5, #16, #4
>> e1a00008        mov     r0, r8
>> e1a09001        mov     r9, r1
>> e1a04002        mov     r4, r2
>> ebf35462        bl      c03c6530 <__asan_load4>
>> e357000f        cmp     r7, #15
>> e7e36655        ubfx    r6, r5, #12, #4
>> e205a00f        and     sl, r5, #15
>> 0a000001        beq     c06f13bc <emulate_ldr+0x38>
>> e0840107        add     r0, r4, r7, lsl #2
>> ebf3545c        bl      c03c6530 <__asan_load4>
>> e084010a        add     r0, r4, sl, lsl #2
>> ebf3545a        bl      c03c6530 <__asan_load4>
>> e2890010        add     r0, r9, #16
>> ebf35458        bl      c03c6530 <__asan_load4>
>> e5990010        ldr     r0, [r9, #16]
>> e12fff30        blx     r0
>> e356000f        cm      r6, #15
>> 1a000014        bne     c06f1430 <emulate_ldr+0xac>
>> e1a06000        mov     r6, r0
>> e2840040        add     r0, r4, #64     ; 0x40
>> ......
>>
>> when running in emulate_ldr to simulate the ldr instruction, panic
>> occurred, and the log is as follows:
>> Unable to handle kernel NULL pointer dereference at virtual address
>> 00000090
>> pgd = ecb46400
>> [00000090] *pgd=2e0fa003, *pmd=00000000
>> Internal error: Oops: 206 [#1] SMP ARM
>> PC is at cap_capable+0x14/0xb0
>> LR is at emulate_ldr+0x50/0xc0
>> psr: 600d0293 sp : ecd63af8  ip : 00000004  fp : c0a7c30c
>> r10: 00000000  r9 : c30897f4  r8 : ecd63cd4
>> r7 : 0000000f  r6 : 0000000a  r5 : e59fa090  r4 : ecd63c98
>> r3 : c06ae294  r2 : 00000000  r1 : b7611300  r0 : bf4ec008
>> Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
>> Control: 32c5387d  Table: 2d546400  DAC: 55555555
>> Process bash (pid: 1643, stack limit = 0xecd60190)
>> (cap_capable) from (kprobe_handler+0x218/0x340)
>> (kprobe_handler) from (kprobe_trap_handler+0x24/0x48)
>> (kprobe_trap_handler) from (do_undefinstr+0x13c/0x364)
>> (do_undefinstr) from (__und_svc_finish+0x0/0x30)
>> (__und_svc_finish) from (cap_capable+0x18/0xb0)
>> (cap_capable) from (cap_vm_enough_memory+0x38/0x48)
>> (cap_vm_enough_memory) from
>> (security_vm_enough_memory_mm+0x48/0x6c)
>> (security_vm_enough_memory_mm) from
>> (copy_process.constprop.5+0x16b4/0x25c8)
>> (copy_process.constprop.5) from (_do_fork+0xe8/0x55c)
>> (_do_fork) from (SyS_clone+0x1c/0x24)
>> (SyS_clone) from (__sys_trace_return+0x0/0x10)
>> Code: 0050a0e1 6c0080e2 0140a0e1 0260a0e1 (f801f0e7)
>>
>> Fixes: 35aa1df43283 ("ARM kprobes: instruction single-stepping support")
>> Fixes: 421015713b30 ("ARM: 9017/2: Enable KASan for ARM")
>> Signed-off-by: huangshaobo <huangshaobo6@xxxxxxxxxx>
>> Asked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> 
> Please don't do this - the maintainer will pick it up when applying,
> or when you send a new version of the patch, it is OK to add these
> tags if you have not made any substantial changes.
> 
> But please do *not* add tags like this on someone else's behalf by
> replying to the email - and I should also point out that 'asked-by' is
> bogus.
> 

Hi ardb,
1.The original patch you have been asked-by by email before, link: https://lore.kernel.org/linux-arm-kernel/CAMj1kXGqfF68MT4WwrxS0cYiUBb0gODDh-wGZSQcW9vxdfK90A@xxxxxxxxxxxxxx/
2.In addition to adding the asked-by tag, there is no other content modification in this patch
3.The patch was reissued because the previous recipient did not include kasan maintainer and reviewers

thanks,
ShaoBo Huang

>
>> ---
>>  arch/arm/probes/kprobes/Makefile | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/probes/kprobes/Makefile b/arch/arm/probes/kprobes/Makefile
>> index 14db56f49f0a..6159010dac4a 100644
>> --- a/arch/arm/probes/kprobes/Makefile
>> +++ b/arch/arm/probes/kprobes/Makefile
>> @@ -1,4 +1,7 @@
>>  # SPDX-License-Identifier: GPL-2.0
>> +KASAN_SANITIZE_actions-common.o := n
>> +KASAN_SANITIZE_actions-arm.o := n
>> +KASAN_SANITIZE_actions-thumb.o := n
>>  obj-$(CONFIG_KPROBES)          += core.o actions-common.o checkers-common.o
>>  obj-$(CONFIG_ARM_KPROBES_TEST) += test-kprobes.o
>>  test-kprobes-objs              := test-core.o
>> --
>> 2.12.3
>>