Re: [PATCH 1/2] KVM: arm64: Dump instruction on hyp panic

[Mostafa Saleh <smostafa@google.com>]

On Mon, Sep 08, 2025 at 01:16:45PM +0100, Will Deacon wrote:
> On Thu, Jul 17, 2025 at 11:47:43PM +0000, Mostafa Saleh wrote:
> > Similar to the kernel panic, where the instruction code is printed,
> > we can do the same for hypervisor panics.
> > 
> > This patch does that only in case of “CONFIG_NVHE_EL2_DEBUG” or nvhe.
> > 
> > The next patch adds support for pKVM.
> > 
> > Also, remove the hardcoded argument dump_kernel_instr().
> > 
> > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> > ---
> >  arch/arm64/include/asm/traps.h |  1 +
> >  arch/arm64/kernel/traps.c      | 20 +++++++++++++-------
> >  arch/arm64/kvm/handle_exit.c   |  5 +++++
> >  3 files changed, 19 insertions(+), 7 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
> > index 82cf1f879c61..0d7e86a95d62 100644
> > --- a/arch/arm64/include/asm/traps.h
> > +++ b/arch/arm64/include/asm/traps.h
> > @@ -30,6 +30,7 @@ void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *
> >  void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str);
> >  
> >  int early_brk64(unsigned long addr, unsigned long esr, struct pt_regs *regs);
> > +void dump_instr(unsigned long addr);
> >  
> >  /*
> >   * Move regs->pc to next instruction and do necessary setup before it
> > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> > index 9bfa5c944379..d692c05e3686 100644
> > --- a/arch/arm64/kernel/traps.c
> > +++ b/arch/arm64/kernel/traps.c
> > @@ -149,15 +149,11 @@ pstate_check_t * const aarch32_opcode_cond_checks[16] = {
> >  
> >  int show_unhandled_signals = 0;
> >  
> > -static void dump_kernel_instr(const char *lvl, struct pt_regs *regs)
> > +void dump_instr(unsigned long addr)
> >  {
> > -	unsigned long addr = instruction_pointer(regs);
> >  	char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
> >  	int i;
> >  
> > -	if (user_mode(regs))
> > -		return;
> > -
> >  	for (i = -4; i < 1; i++) {
> >  		unsigned int val, bad;
> 
> I'm a little worried that this function might be used to try and dump
> instructions from userspace now that it just takes an address.
> 
> Maybe we could:
> 
>   - Keep the name unchanged, e.g. void dump_kernel_instr(unsigned long kaddr)
>   - Inline the user_mode(regs) and instruction_pointer(regs) calls into
>     __die()
>   - Check is_ttbr1_addr(kaddr) in dump_kernel_instr()
> 
> WDYT?

Makes sense, I will do that and respin v2.

Thanks,
Mostafa

> 
> Will