Christophe Leroy <christophe.le...@c-s.fr> writes:
> ping
>
>
> Le 18/02/2020 à 20:38, Christophe Leroy a écrit :
>> When a program check exception happens while MMU translation is
>> disabled, following Oops happens in kprobe_handler() in the following
>> code:
>
> Michael, we have several traps in assembly while MMU is still disabled
> (TRACE_IRQFLAGS, KUAP DEBUG, syscall from kernel, machine check in RTAS,
> ...).
> Without this fix, all of them trigger an Oops when CONFIG_KPROBE is set.
Only on 32-bit.
But I guess this fix is good, if someone really wants to handle kprobes
in real mode they can tell us and do the work to make it solid.
cheers
>> } else if (*addr != BREAKPOINT_INSTRUCTION) {
>>
>> [ 33.098554] BUG: Unable to handle kernel data access on read at 0x0000e268
>> [ 33.105091] Faulting instruction address: 0xc000ec34
>> [ 33.110010] Oops: Kernel access of bad area, sig: 11 [#1]
>> [ 33.115348] BE PAGE_SIZE=16K PREEMPT CMPC885
>> [ 33.119540] Modules linked in:
>> [ 33.122591] CPU: 0 PID: 429 Comm: cat Not tainted
>> 5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267
>> [ 33.131005] NIP: c000ec34 LR: c000ecd8 CTR: c019cab8
>> [ 33.136002] REGS: ca4d3b58 TRAP: 0300 Not tainted
>> (5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)
>> [ 33.144324] MSR: 00001032 <ME,IR,DR,RI> CR: 2a4d3c52 XER: 00000000
>> [ 33.150699] DAR: 0000e268 DSISR: c0000000
>> [ 33.150699] GPR00: c000b09c ca4d3c10 c66d0620 00000000 ca4d3c60 00000000
>> 00009032 00000000
>> [ 33.150699] GPR08: 00020000 00000000 c087de44 c000afe0 c66d0ad0 100d3dd6
>> fffffff3 00000000
>> [ 33.150699] GPR16: 00000000 00000041 00000000 ca4d3d70 00000000 00000000
>> 0000416d 00000000
>> [ 33.150699] GPR24: 00000004 c53b6128 00000000 0000e268 00000000 c07c0000
>> c07bb6fc ca4d3c60
>> [ 33.188015] NIP [c000ec34] kprobe_handler+0x128/0x290
>> [ 33.192989] LR [c000ecd8] kprobe_handler+0x1cc/0x290
>> [ 33.197854] Call Trace:
>> [ 33.200340] [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
>> [ 33.206590] [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
>> [ 33.212392] --- interrupt: 700 at 0xe268
>> [ 33.270401] Instruction dump:
>> [ 33.273335] 913e0008 81220000 38600001 3929ffff 91220000 80010024
>> bb410008 7c0803a6
>> [ 33.280992] 38210020 4e800020 38600000 4e800020 <813b0000> 6d2a7fe0
>> 2f8a0008 419e0154
>> [ 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 or MSR_DR cleared, return 0 immediately.
>>
>> Reported-by: Larry Finger <larry.fin...@lwfinger.net>
>> Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
>> Cc: sta...@vger.kernel.org
>> Cc: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
>> Cc: Masami Hiramatsu <mhira...@kernel.org>
>> Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
>>
>> ---
>> v3: Also bail out if MSR_DR is cleared.
>>
>> Resending v2 with a more appropriate name
>>
>> 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.le...@c-s.fr>
>> ---
>> arch/powerpc/kernel/kprobes.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
>> index 2d27ec4feee4..9b340af02c38 100644
>> --- a/arch/powerpc/kernel/kprobes.c
>> +++ b/arch/powerpc/kernel/kprobes.c
>> @@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
>> if (user_mode(regs))
>> return 0;
>>
>> + if (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR))
>> + return 0;
>> +
>> /*
>> * We don't want to be preempted for the entire
>> * duration of kprobe processing
>>
