Re: Fix BUG_ON() reporting in real mode on powerpc
From: Aneesh Kumar K.V <hidden>
Date: 2016-02-17 15:16:35
Balbir Singh [off-list ref] writes:
quoted hunk ↗ jump to hunk
quoted
It might be a little better to do this: =20 bugaddr =3D regs->nip; if (REGION_ID(bugaddr) =3D=3D 0 && !(regs->msr & MSR_IR)) bugaddr +=3D PAGE_OFFSET; =20 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 <redacted> Signed-off-by: Balbir Singh <bsingharora@gmail.com> --- =C2=A0arch/powerpc/kernel/traps.c | 7 ++++++- =C2=A01 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_re=
gs *regs)
quoted hunk ↗ jump to hunk
=C2=A0 goto bail; =C2=A0 } =C2=A0 if (reason & REASON_TRAP) { + unsigned long bugaddr; =C2=A0 /* Debugger is first in line to stop recursive faults in =C2=A0 =C2=A0* rcu_lock, notify_die, or atomic_notifier_call_chain */ =C2=A0 if (debugger_bpt(regs))@@ -1158,8 +1159,12 @@ void __kprobes program_check_exception(struct pt_r=
egs *regs)
=C2=A0 =3D=3D NOTIFY_STOP) =C2=A0 goto bail; =C2=A0 + bugaddr =3D regs->nip; + if ((REGION_ID(bugaddr) =3D=3D 0) && !(regs->msr & MSR_IR)) + bugaddr +=3D 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.
=C2=A0 if (!(regs->msr & MSR_PR) &&=C2=A0=C2=A0/* not user-mode */ - =C2=A0=C2=A0=C2=A0=C2=A0report_bug(regs->nip, regs) =3D=3D BUG_TRAP_TY=
PE_WARN) {+ =C2=A0=C2=A0=C2=A0=C2=A0report_bug(bugaddr, regs) =3D=3D BUG_TRAP_TYPE=
_WARN) {=C2=A0 regs->nip +=3D 4; =C2=A0 goto bail; =C2=A0 } --=C2=A0
-aneesh