Messages in this thread | | | Subject | Re: [PATCH] x86/split_lock: Sanitize userspace and guest error output | From | Prarit Bhargava <> | Date | Fri, 5 Jun 2020 12:42:45 -0400 |
| |
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.
| |