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    SubjectRe: [PATCH] riscv: kprobe: Fixup kernel panic when probing an illegal position
    On Tue, Jan 31, 2023 at 8:32 PM Björn Töpel <bjorn@kernel.org> wrote:
    >
    > guoren@kernel.org writes:
    >
    > > From: Guo Ren <guoren@linux.alibaba.com>
    > >
    > > The kernel would panic when probed for an illegal position. eg:
    > >
    > > (CONFIG_RISCV_ISA_C=n)
    > >
    > > echo 'p:hello kernel_clone+0x16 a0=%a0' >> kprobe_events
    > > echo 1 > events/kprobes/hello/enable
    > > cat trace
    > >
    > > Kernel panic - not syncing: stack-protector: Kernel stack
    > > is corrupted in: __do_sys_newfstatat+0xb8/0xb8
    > > CPU: 0 PID: 111 Comm: sh Not tainted
    > > 6.2.0-rc1-00027-g2d398fe49a4d #490
    > > Hardware name: riscv-virtio,qemu (DT)
    > > Call Trace:
    > > [<ffffffff80007268>] dump_backtrace+0x38/0x48
    > > [<ffffffff80c5e83c>] show_stack+0x50/0x68
    > > [<ffffffff80c6da28>] dump_stack_lvl+0x60/0x84
    > > [<ffffffff80c6da6c>] dump_stack+0x20/0x30
    > > [<ffffffff80c5ecf4>] panic+0x160/0x374
    > > [<ffffffff80c6db94>] generic_handle_arch_irq+0x0/0xa8
    > > [<ffffffff802deeb0>] sys_newstat+0x0/0x30
    > > [<ffffffff800158c0>] sys_clone+0x20/0x30
    > > [<ffffffff800039e8>] ret_from_syscall+0x0/0x4
    > > ---[ end Kernel panic - not syncing: stack-protector:
    > > Kernel stack is corrupted in: __do_sys_newfstatat+0xb8/0xb8 ]---
    > >
    > > That is because the kprobe's ebreak instruction broke the kernel's
    > > original code. The user should guarantee the correction of the probe
    > > position, but it couldn't make the kernel panic.
    > >
    > > This patch adds arch_check_kprobe in arch_prepare_kprobe to prevent an
    > > illegal position (Such as the middle of an instruction).
    >
    > Nice!
    >
    > @liaochang Will you remove your patch from the OPTPROBE series?
    >
    > > Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
    > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
    > > Signed-off-by: Guo Ren <guoren@kernel.org>
    > > ---
    > > arch/riscv/kernel/probes/kprobes.c | 18 ++++++++++++++++++
    > > 1 file changed, 18 insertions(+)
    > >
    > > diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
    > > index f21592d20306..475989f06d6d 100644
    > > --- a/arch/riscv/kernel/probes/kprobes.c
    > > +++ b/arch/riscv/kernel/probes/kprobes.c
    > > @@ -48,6 +48,21 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
    > > post_kprobe_handler(p, kcb, regs);
    > > }
    > >
    > > +static bool __kprobes arch_check_kprobe(struct kprobe *p)
    > > +{
    > > + unsigned long tmp = (unsigned long)p->addr - p->offset;
    > > + unsigned long addr = (unsigned long)p->addr;
    > > +
    > > + while (tmp <= addr) {
    > > + if (tmp == addr)
    > > + return true;
    > > +
    > > + tmp += GET_INSN_LENGTH(*(kprobe_opcode_t *)tmp);
    >
    > kprobe_opcode_t is u32; This can trigger a misaligned load, right?
    >
    > > + }
    > > +
    > > + return false;
    > > +}
    > > +
    > > int __kprobes arch_prepare_kprobe(struct kprobe *p)
    > > {
    > > unsigned long probe_addr = (unsigned long)p->addr;
    > > @@ -55,6 +70,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
    > > if (probe_addr & 0x1)
    > > return -EILSEQ;
    > >
    > > + if (!arch_check_kprobe(p))
    > > + return -EILSEQ;
    > > +
    > > /* copy instruction */
    > > p->opcode = *p->addr;
    >
    > Not related to your patch, but this can also trigger a misaligned load.
    After rereading the spec, misaligned load/store is not mandatory
    supported. (Although my machines and qemu are correct)

    So I need fixup:

    diff --git a/arch/riscv/kernel/probes/kprobes.c
    b/arch/riscv/kernel/probes/kprobes.c
    index 27f8960c321c..0c016d496746 100644
    --- a/arch/riscv/kernel/probes/kprobes.c
    +++ b/arch/riscv/kernel/probes/kprobes.c
    @@ -58,12 +58,14 @@ static bool __kprobes arch_check_kprobe(struct kprobe *p)
    {
    unsigned long tmp = (unsigned long)p->addr - p->offset;
    unsigned long addr = (unsigned long)p->addr;
    + kprobe_opcode_t opcode;

    while (tmp <= addr) {
    if (tmp == addr)
    return true;

    - tmp += GET_INSN_LENGTH(*(kprobe_opcode_t *)tmp);
    + memcpy(&opcode, (void *)tmp, sizeof(kprobe_opcode_t));
    + tmp += GET_INSN_LENGTH(opcode);
    }

    return false;
    @@ -80,7 +82,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
    return -EILSEQ;

    /* copy instruction */
    - p->opcode = *p->addr;
    + memcpy(&p->opcode, p->addr, sizeof(kprobe_opcode_t));

    /* decode instruction */
    switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
    >
    >
    > Björn



    --
    Best Regards
    Guo Ren

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