[External] Re: [PATCH v3] riscv: add userland instruction dump to RISC-V splats

[yunhui cui]

Hi Björn，

On Thu, Aug 17, 2023 at 9:27 PM Björn Töpel <bjorn at kernel.org> wrote:
>
> Yunhui Cui <cuiyunhui at bytedance.com> writes:
>
> > Added userland instruction dump in dump_kernel_instr().
> >
> > An example:
> > [    0.822439] Freeing unused kernel image (initmem) memory: 6916K
> > [    0.823817] Run /init as init process
> > [    0.839411] init[1]: unhandled signal 4 code 0x1 at 0x000000000005be18 in bb[10000+5fb000]
> > [    0.840751] CPU: 0 PID: 1 Comm: init Not tainted 5.14.0-rc4-00049-gbd644290aa72-dirty #187
> > [    0.841373] Hardware name:  , BIOS
> > [    0.841743] epc : 000000000005be18 ra : 0000000000079e74 sp : 0000003fffcafda0
> > [    0.842271]  gp : ffffffff816e9dc8 tp : 0000000000000000 t0 : 0000000000000000
> > [    0.842947]  t1 : 0000003fffc9fdf0 t2 : 0000000000000000 s0 : 0000000000000000
> > [    0.843434]  s1 : 0000000000000000 a0 : 0000003fffca0190 a1 : 0000003fffcafe18
> > [    0.843891]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
> > [    0.844357]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000000000000
> > [    0.844803]  s2 : 0000000000000000 s3 : 0000000000000000 s4 : 0000000000000000
> > [    0.845253]  s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
> > [    0.845722]  s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000000000000000
> > [    0.846180]  s11: 0000000000d144e0 t3 : 0000000000000000 t4 : 0000000000000000
> > [    0.846616]  t5 : 0000000000000000 t6 : 0000000000000000
> > [    0.847204] status: 0000000200000020 badaddr: 00000000f0028053 cause: 0000000000000002
> > [    0.848219] Code: f06f ff5f 3823 fa11 0113 fb01 2e23 0201 0293 0000 (8053) f002
> > [    0.851016] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
> >
> > Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
> > ---
> >  arch/riscv/kernel/traps.c | 10 +++++++---
> >  include/linux/uaccess.h   |  5 +++++
> >  2 files changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > index f910dfccbf5d..a6a850e42d59 100644
> > --- a/arch/riscv/kernel/traps.c
> > +++ b/arch/riscv/kernel/traps.c
> > @@ -33,7 +33,7 @@ int show_unhandled_signals = 1;
> >
> >  static DEFINE_SPINLOCK(die_lock);
> >
> > -static void dump_kernel_instr(const char *loglvl, struct pt_regs *regs)
> > +static void dump_instr(const char *loglvl, struct pt_regs *regs)
> >  {
> >       char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
> >       const u16 *insns = (u16 *)instruction_pointer(regs);
> > @@ -42,7 +42,10 @@ static void dump_kernel_instr(const char *loglvl, struct pt_regs *regs)
> >       int i;
> >
> >       for (i = -10; i < 2; i++) {
> > -             bad = get_kernel_nofault(val, &insns[i]);
> > +             if (user_mode(regs))
> > +                     bad = get_user_nofault(val, &insns[i]);
> > +             else
> > +                     bad = get_kernel_nofault(val, &insns[i]);
> >               if (!bad) {
> >                       p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
> >               } else {
> > @@ -71,7 +74,7 @@ void die(struct pt_regs *regs, const char *str)
> >       print_modules();
> >       if (regs) {
> >               show_regs(regs);
> > -             dump_kernel_instr(KERN_EMERG, regs);
> > +             dump_instr(KERN_EMERG, regs);
> >       }
> >
> >       cause = regs ? regs->cause : -1;
> > @@ -104,6 +107,7 @@ void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
> >               print_vma_addr(KERN_CONT " in ", instruction_pointer(regs));
> >               pr_cont("\n");
> >               __show_regs(regs);
> > +             dump_instr(KERN_EMERG, regs);
> >       }
> >
> >       force_sig_fault(signo, code, (void __user *)addr);
> > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> > index 3064314f4832..ba8cb37a7241 100644
> > --- a/include/linux/uaccess.h
> > +++ b/include/linux/uaccess.h
> > @@ -385,6 +385,11 @@ long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
> >               long count);
> >  long strnlen_user_nofault(const void __user *unsafe_addr, long count);
> >
> > +#define get_user_nofault(val, ptr) ({                                \
> > +     const typeof(val) *__gk_ptr = (ptr);                    \
> > +     copy_from_user_nofault(&(val), __gk_ptr, sizeof(val));\
> > +})
> > +
>
> Your previous version had a check:
>   |         /* The user space code from other tasks cannot be accessed. */
>   |         if (regs != task_pt_regs(current))
>   |                 return -EPERM;
>
> Why was that left out? Is it not needed?
>
> Your get_user_nofault is only used in this file, so maybe it's better to
> do what x86 does, and introduce a static "copy_code()" that deals with
> the user/kernel checks/copy?
Okay， i‘ll update it to v4.

Thanks，
Yunhui