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

[Ard Biesheuvel]

On Mon, 19 Jul 2021 at 05:09, Shaobo Huang <huangshaobo6 at huawei.com> wrote:
>
> On Sat, 17 Jul 2021 at 01:01, Ard Biesheuvel <ardb at kernel.org> wrote:
> > On Wed, 14 Jul 2021 at 10:27, Shaobo Huang <huangshaobo6 at huawei.com> wrote:
> >>
> >> From: huangshaobo <huangshaobo6 at huawei.com>
> >>
> >> 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 at huawei.com>
> >> Asked-by: Ard Biesheuvel <ardb at kernel.org>
> >
> > 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@mail.gmail.com/

No it was not.

It was ACKed by, not ASKed by.

> 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
>

I don't care. Do NOT reply to emails with tags in other people's names.


> 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
> >>