Balbir Singh <bsinghar...@gmail.com> writes:
>> It might be a little better to do this:
>>
>> bugaddr = regs->nip;
>> if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR))
>> bugaddr += PAGE_OFFSET;
>>
>> It is possible to execute from addresses with the 0xc000... on top in
>> real mode, because the CPU ignores the top 4 address bits in real
>> mode.
>
> Good catch! Thank you
>
> Changelog:
> Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
>
> I ran into this issue while debugging an early boot problem.
> The system hit a BUG_ON() but report bug failed to print the
> line number and file name. The reason being that the system
> was running in real mode and report_bug() searches for
> addresses in the PAGE_OFFSET+ region
>
> Suggested-by: Paul Mackerras <pau...@samba.org>
> Signed-off-by: Balbir Singh <bsinghar...@gmail.com>
> ---
> arch/powerpc/kernel/traps.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index b6becc7..4de4fe7 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -1148,6 +1148,7 @@ void __kprobes program_check_exception(struct pt_regs
> *regs)
> goto bail;
> }
> if (reason & REASON_TRAP) {
> + unsigned long bugaddr;
> /* Debugger is first in line to stop recursive faults in
> * rcu_lock, notify_die, or atomic_notifier_call_chain */
> if (debugger_bpt(regs))
> @@ -1158,8 +1159,12 @@ void __kprobes program_check_exception(struct pt_regs
> *regs)
> == NOTIFY_STOP)
> goto bail;
>
> + bugaddr = regs->nip;
> + if ((REGION_ID(bugaddr) == 0) && !(regs->msr & MSR_IR))
> + bugaddr += PAGE_OFFSET;
> +
Can we add some comments around this. When i looked at this first, i was
wondering how nip can be in user region. But then realized that what we
are checking here is kernel address used in real mode. The use of
REGION_ID eventhough simpler is confusing. Hence adding the comment with
details Paul mentioned in email will help.
> if (!(regs->msr & MSR_PR) && /* not user-mode */
> - report_bug(regs->nip, regs) == BUG_TRAP_TYPE_WARN) {
> + report_bug(bugaddr, regs) == BUG_TRAP_TYPE_WARN) {
> regs->nip += 4;
> goto bail;
> }
> --
-aneesh
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