From: Prarit Bhargava <prarit@redhat.com>
To: Xiaoyao Li <xiaoyao.li@intel.com>, linux-kernel@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Tony Luck <tony.luck@intel.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Rahul Tanwar <rahul.tanwar@linux.intel.com>,
Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH] x86/split_lock: Sanitize userspace and guest error output
Date: Fri, 5 Jun 2020 12:42:45 -0400 [thread overview]
Message-ID: <3e1f1fac-fa46-7a2a-1424-d5c931e521d7@redhat.com> (raw)
In-Reply-To: <96b5c5fa-6b4e-a5f4-34cc-682477a27370@intel.com>
On 6/5/20 11:29 AM, Xiaoyao Li wrote:
> On 6/5/2020 7:44 PM, Prarit Bhargava wrote:
>> There are two problems with kernel messages in fatal mode that
>> were found during testing of guests and userspace programs.
>>
>> The first is that no kernel message is output when the split lock detector
>> is triggered with a userspace program. As a result the userspace process
>> dies from receiving SIGBUS with no indication to the user of what caused
>> the process to die.
>>
>> The second problem is that only the first triggering guest causes a kernel
>> message to be output because the message is output with pr_warn_once().
>> This also results in a loss of information to the user.
>>
>> While fixing these I noticed that the same message was being output
>> three times so I'm cleaning that up too.
>>
>> Fix fatal mode output, and use consistent messages for fatal and
>> warn modes for both userspace and guests.
>>
>> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Borislav Petkov <bp@alien8.de>
>> Cc: x86@kernel.org
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: Tony Luck <tony.luck@intel.com>
>> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
>> Cc: Sean Christopherson <sean.j.christopherson@intel.com>
>> Cc: Rahul Tanwar <rahul.tanwar@linux.intel.com>
>> Cc: Xiaoyao Li <xiaoyao.li@intel.com>
>> Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> ---
>> arch/x86/kernel/cpu/intel.c | 24 ++++++++++--------------
>> 1 file changed, 10 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
>> index 166d7c355896..463022aa9b7a 100644
>> --- a/arch/x86/kernel/cpu/intel.c
>> +++ b/arch/x86/kernel/cpu/intel.c
>> @@ -1074,10 +1074,14 @@ static void split_lock_init(void)
>> split_lock_verify_msr(sld_state != sld_off);
>> }
>> -static void split_lock_warn(unsigned long ip)
>> +static bool split_lock_warn(unsigned long ip, int fatal)
>> {
>> - pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
>> - current->comm, current->pid, ip);
>> + pr_warn_ratelimited("#AC: %s/%d %ssplit_lock trap at address: 0x%lx\n",
>> + current->comm, current->pid,
>> + sld_state == sld_fatal ? "fatal " : "", ip);
>> +
>> + if (sld_state == sld_fatal || fatal)
>> + return false;
>> /*
>> * Disable the split lock detection for this task so it can make
>> @@ -1086,18 +1090,13 @@ static void split_lock_warn(unsigned long ip)
>> */
>> sld_update_msr(false);
>> set_tsk_thread_flag(current, TIF_SLD);
>> + return true;
>> }
>> bool handle_guest_split_lock(unsigned long ip)
>> {
>> - if (sld_state == sld_warn) {
>> - split_lock_warn(ip);
>> + if (split_lock_warn(ip, 0))
>> return true;
>> - }
>> -
>> - pr_warn_once("#AC: %s/%d %s split_lock trap at address: 0x%lx\n",
>> - current->comm, current->pid,
>> - sld_state == sld_fatal ? "fatal" : "bogus", ip);
>> current->thread.error_code = 0;
>> current->thread.trap_nr = X86_TRAP_AC;
>> @@ -1108,10 +1107,7 @@ EXPORT_SYMBOL_GPL(handle_guest_split_lock);
>> bool handle_user_split_lock(struct pt_regs *regs, long error_code)
>> {
>> - if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
>> - return false;
>> - split_lock_warn(regs->ip);
>> - return true;
>> + return split_lock_warn(regs->ip, regs->flags & X86_EFLAGS_AC);
>
> It's incorrect. You change the behavior that it will print the split lock
> warning even when CPL 3 Alignment Check is turned on.
Do you want the message to be displayed in the fatal case of CPL 3 Alignment check?
P.
next prev parent reply other threads:[~2020-06-05 16:42 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-05 11:44 [PATCH] x86/split_lock: Sanitize userspace and guest error output Prarit Bhargava
2020-06-05 15:29 ` Xiaoyao Li
2020-06-05 16:42 ` Prarit Bhargava [this message]
2020-06-06 3:02 ` Xiaoyao Li
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