Re: [PATCH v2] powerpc/kprobes: Fix trap address when trap happened in real mode

[Christophe Leroy]

Le 18/02/2020 Ã 15:55, Naveen N. Rao a ÃcritÂ:
> Christophe Leroy wrote:
> > When a program check exception happens while MMU translation is
> > disabled, following Oops happens in kprobe_handler() in the following
> > code:
> >
> > ÂÂÂÂÂÂÂ } else if (*addr != BREAKPOINT_INSTRUCTION) {
> >
> > [ÂÂ 33.098554] BUG: Unable to handle kernel data access on read at 
> > 0x0000e268
> > [ÂÂ 33.105091] Faulting instruction address: 0xc000ec34
> > [ÂÂ 33.110010] Oops: Kernel access of bad area, sig: 11 [#1]
> > [ÂÂ 33.115348] BE PAGE_SIZE=16K PREEMPT CMPC885
> > [ÂÂ 33.119540] Modules linked in:
> > [ÂÂ 33.122591] CPU: 0 PID: 429 Comm: cat Not tainted 
> > 5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267
> > [ÂÂ 33.131005] NIP:Â c000ec34 LR: c000ecd8 CTR: c019cab8
> > [ÂÂ 33.136002] REGS: ca4d3b58 TRAP: 0300ÂÂ Not tainted  
> > (5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)
> > [ÂÂ 33.144324] MSR:Â 00001032 <ME,IR,DR,RI>Â CR: 2a4d3c52Â XER: 00000000
> > [ÂÂ 33.150699] DAR: 0000e268 DSISR: c0000000
> > [ÂÂ 33.150699] GPR00: c000b09c ca4d3c10 c66d0620 00000000 ca4d3c60 
> > 00000000 00009032 00000000
> > [ÂÂ 33.150699] GPR08: 00020000 00000000 c087de44 c000afe0 c66d0ad0 
> > 100d3dd6 fffffff3 00000000
> > [ÂÂ 33.150699] GPR16: 00000000 00000041 00000000 ca4d3d70 00000000 
> > 00000000 0000416d 00000000
> > [ÂÂ 33.150699] GPR24: 00000004 c53b6128 00000000 0000e268 00000000 
> > c07c0000 c07bb6fc ca4d3c60
> > [ÂÂ 33.188015] NIP [c000ec34] kprobe_handler+0x128/0x290
> > [ÂÂ 33.192989] LR [c000ecd8] kprobe_handler+0x1cc/0x290
> > [ÂÂ 33.197854] Call Trace:
> > [ÂÂ 33.200340] [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
> > [ÂÂ 33.206590] [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
> > [ÂÂ 33.212392] --- interrupt: 700 at 0xe268
> > [ÂÂ 33.270401] Instruction dump:
> > [ÂÂ 33.273335] 913e0008 81220000 38600001 3929ffff 91220000 80010024 
> > bb410008 7c0803a6
> > [ÂÂ 33.280992] 38210020 4e800020 38600000 4e800020 <813b0000> 6d2a7fe0 
> > 2f8a0008 419e0154
> > [ÂÂ 33.288841] ---[ end trace 5b9152d4cdadd06d ]---
> >
> > kprobe is not prepared to handle events in real mode and functions
> > running in real mode should have been blacklisted, so kprobe_handler()
> > can safely bail out telling 'this trap is not mine' for any trap that
> > happened while in real-mode.
> >
> > If the trap happened with MSR_IR cleared, return 0 immediately.
> >
> > Reported-by: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
> > Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> >
> > ---
> > v2: bailing out instead of converting real-time address to virtual and 
> > continuing.
> >
> > The bug might have existed even before that commit from Naveen.
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> > ---
> > Âarch/powerpc/kernel/kprobes.c | 3 +++
> > Â1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/powerpc/kernel/kprobes.c 
> > b/arch/powerpc/kernel/kprobes.c
> > index 2d27ec4feee4..673f349662e8 100644
> > --- a/arch/powerpc/kernel/kprobes.c
> > +++ b/arch/powerpc/kernel/kprobes.c
> > @@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
> > ÂÂÂÂ if (user_mode(regs))
> > ÂÂÂÂÂÂÂÂ return 0;
> >
> > +ÂÂÂ if (!(regs->msr & MSR_IR))
> > +ÂÂÂÂÂÂÂ return 0;
> > +
>
> Should we also check for MSR_DR? Are there scenarios with ppc32 where 
> MSR_IR is on, but MSR_DR is off?

Yes indeed.

Christophe