x86/mce: Move the tainting outside of the noinstr region

add_taint() is yet another external facility which the #MC handler
calls. Move that tainting call into the instrumentation-allowed part of
the handler.

Fixes

  vmlinux.o: warning: objtool: do_machine_check()+0x617: call to add_taint() leaves .noinstr.text section

While at it, allow instrumentation around the mce_log() call.

Fixes

  vmlinux.o: warning: objtool: do_machine_check()+0x690: call to mce_log() leaves .noinstr.text section

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211208111343.8130-11-bp@alien8.de

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 53b4cfc..044c94b 100644 (file)
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1180,13 +1180,14 @@ static noinstr bool mce_check_crashing_cpu(void)
        return false;
 }
 
-static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *final,
-                           unsigned long *toclear, unsigned long *valid_banks,
-                           int no_way_out, int *worst)
+static __always_inline int
+__mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *final,
+               unsigned long *toclear, unsigned long *valid_banks, int no_way_out,
+               int *worst)
 {
        struct mce_bank *mce_banks = this_cpu_ptr(mce_banks_array);
        struct mca_config *cfg = &mca_cfg;
-       int severity, i;
+       int severity, i, taint = 0;
 
        for (i = 0; i < this_cpu_read(mce_num_banks); i++) {
                __clear_bit(i, toclear);
@@ -1213,7 +1214,7 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
                        continue;
 
                /* Set taint even when machine check was not enabled. */
-               add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+               taint++;
 
                severity = mce_severity(m, regs, cfg->tolerant, NULL, true);
 
@@ -1236,7 +1237,13 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
                /* assuming valid severity level != 0 */
                m->severity = severity;
 
+               /*
+                * Enable instrumentation around the mce_log() call which is
+                * done in #MC context, where instrumentation is disabled.
+                */
+               instrumentation_begin();
                mce_log(m);
+               instrumentation_end();
 
                if (severity > *worst) {
                        *final = *m;
@@ -1246,6 +1253,8 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
 
        /* mce_clear_state will clear *final, save locally for use later */
        *m = *final;
+
+       return taint;
 }
 
 static void kill_me_now(struct callback_head *ch)
@@ -1362,7 +1371,7 @@ static noinstr void unexpected_machine_check(struct pt_regs *regs)
  */
 noinstr void do_machine_check(struct pt_regs *regs)
 {
-       int worst = 0, order, no_way_out, kill_current_task, lmce;
+       int worst = 0, order, no_way_out, kill_current_task, lmce, taint = 0;
        DECLARE_BITMAP(valid_banks, MAX_NR_BANKS) = { 0 };
        DECLARE_BITMAP(toclear, MAX_NR_BANKS) = { 0 };
        struct mca_config *cfg = &mca_cfg;
@@ -1441,7 +1450,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
                order = mce_start(&no_way_out);
        }
 
-       __mc_scan_banks(&m, regs, final, toclear, valid_banks, no_way_out, &worst);
+       taint = __mc_scan_banks(&m, regs, final, toclear, valid_banks, no_way_out, &worst);
 
        if (!no_way_out)
                mce_clear_state(toclear);
@@ -1473,17 +1482,19 @@ noinstr void do_machine_check(struct pt_regs *regs)
                }
        }
 
-       if (worst != MCE_AR_SEVERITY && !kill_current_task)
-               goto out;
-
        /*
-        * Enable instrumentation around the external facilities like
-        * task_work_add() (via queue_task_work()), fixup_exception() etc.
-        * For now, that is. Fixing this properly would need a lot more involved
-        * reorganization.
+        * Enable instrumentation around the external facilities like task_work_add()
+        * (via queue_task_work()), fixup_exception() etc. For now, that is. Fixing this
+        * properly would need a lot more involved reorganization.
         */
        instrumentation_begin();
 
+       if (taint)
+               add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+
+       if (worst != MCE_AR_SEVERITY && !kill_current_task)
+               goto out;
+
        /* Fault was in user mode and we need to take some action */
        if ((m.cs & 3) == 3) {
                /* If this triggers there is no way to recover. Die hard. */
@@ -1513,9 +1524,9 @@ noinstr void do_machine_check(struct pt_regs *regs)
                        queue_task_work(&m, msg, kill_me_never);
        }
 
+out:
        instrumentation_end();
 
-out:
        mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
 }
 EXPORT_SYMBOL_GPL(do_machine_check);