From: Balbir Singh <bsingharora@gmail.com>
To: Paul Mackerras <paulus@ozlabs.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org
Subject: Re: Fix BUG_ON() reporting in real mode on powerpc
Date: Wed, 17 Feb 2016 18:16:05 +1100 [thread overview]
Message-ID: <1455693365.3089.8.camel@gmail.com> (raw)
In-Reply-To: <20160217045606.GA19276@oak.ozlabs.ibm.com>
> 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 <paulus@samba.org>
Signed-off-by: Balbir Singh <bsingharora@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;
+
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;
}
--
2.5.0
next prev parent reply other threads:[~2016-02-17 7:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-17 4:43 Fix BUG_ON() reporting in real mode on powerpc Balbir Singh
2016-02-17 4:56 ` Paul Mackerras
2016-02-17 7:16 ` Balbir Singh [this message]
2016-02-17 8:03 ` Anshuman Khandual
2016-02-17 8:23 ` Paul Mackerras
2016-02-17 15:16 ` Aneesh Kumar K.V
2016-02-18 0:25 ` Balbir Singh
2016-02-18 2:41 ` Aneesh Kumar K.V
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