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SubjectRe: [PATCH v5] x86/split_lock: Sanitize userspace and guest error output
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Just re-pinging on this.

P.

On 6/16/20 7:32 AM, 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.
>
> Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> 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>
> ---
> v2: Do not output a message if CPL 3 Alignment Check is turned on (xiaoyao.li)
> v3: refactor code (sean.j.christopherson)
> v4: Fix Sign off (sean.j.christopherson)
> v5: Fix Sign off (sean.j.christopherson)
>
> arch/x86/kernel/cpu/intel.c | 22 ++++++++++------------
> 1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 63926c94eb5f..3a373f0be674 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1074,11 +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 handle_split_lock(unsigned long ip)
> {
> - pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
> + pr_warn("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
> current->comm, current->pid, ip);
>
> + if (sld_state != sld_warn)
> + return false;
> +
> /*
> * Disable the split lock detection for this task so it can make
> * progress and set TIF_SLD so the detection is re-enabled via
> @@ -1086,18 +1089,13 @@ 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 (handle_split_lock(ip))
> 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 +1106,10 @@ 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)
> + if (regs->flags & X86_EFLAGS_AC)
> return false;
> - split_lock_warn(regs->ip);
> - return true;
> +
> + return handle_split_lock(regs->ip);
> }
>
> /*
>

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