linux-kernel - Re: [PATCH] powerpc/traps: fix recoverability of machine check handling on book3s/32

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87pn6sqweq.fsf@mpe.ellerman.id.au>
Date:   Fri, 11 Sep 2020 23:23:57 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michal Suchánek <msuchanek@...e.de>,
        Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/traps: fix recoverability of machine check handling on book3s/32

Michal Suchánek <msuchanek@...e.de> writes:
> Hello,
>
> does this logic apply to "Unrecoverable System Reset" as well?

Which logic do you mean?

We do call die() before checking MSR_RI in system_reset_exception():

  	/*
  	 * No debugger or crash dump registered, print logs then
  	 * panic.
  	 */
  	die("System Reset", regs, SIGABRT);
  
  	mdelay(2*MSEC_PER_SEC); /* Wait a little while for others to print */
  	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
  	nmi_panic(regs, "System Reset");
  
  out:
  #ifdef CONFIG_PPC_BOOK3S_64
  	BUG_ON(get_paca()->in_nmi == 0);
  	if (get_paca()->in_nmi > 1)
  		die("Unrecoverable nested System Reset", regs, SIGABRT);
  #endif
  	/* Must die if the interrupt is not recoverable */
  	if (!(regs->msr & MSR_RI))
  		die("Unrecoverable System Reset", regs, SIGABRT);


So you should see the output from die("System Reset", ...) even if
MSR[RI] was clear when you took the system reset.

cheers

> On Tue, Jan 22, 2019 at 02:11:24PM +0000, Christophe Leroy wrote:
>> Looks like book3s/32 doesn't set RI on machine check, so
>> checking RI before calling die() will always be fatal
>> allthought this is not an issue in most cases.
>> 
>> Fixes: b96672dd840f ("powerpc: Machine check interrupt is a non-maskable interrupt")
>> Fixes: daf00ae71dad ("powerpc/traps: restore recoverability of machine_check interrupts")
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> Cc: stable@...r.kernel.org
>> ---
>>  arch/powerpc/kernel/traps.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
>> index 64936b60d521..c740f8bfccc9 100644
>> --- a/arch/powerpc/kernel/traps.c
>> +++ b/arch/powerpc/kernel/traps.c
>> @@ -763,15 +763,15 @@ void machine_check_exception(struct pt_regs *regs)
>>  	if (check_io_access(regs))
>>  		goto bail;
>>  
>> -	/* Must die if the interrupt is not recoverable */
>> -	if (!(regs->msr & MSR_RI))
>> -		nmi_panic(regs, "Unrecoverable Machine check");
>> -
>>  	if (!nested)
>>  		nmi_exit();
>>  
>>  	die("Machine check", regs, SIGBUS);
>>  
>> +	/* Must die if the interrupt is not recoverable */
>> +	if (!(regs->msr & MSR_RI))
>> +		nmi_panic(regs, "Unrecoverable Machine check");
>> +
>>  	return;
>>  
>>  bail:
>> -- 
>> 2.13.3
>>