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

[Shaobo Huang]

On Thu, 11 Feb 2021 at 09:40, Ard Biesheuvel <ardb@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>

> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

Maintainer ping?

thanks,
ShaoBo Huang