[PATCH v0 10/12] x86/mce: Move the tainting outside of the noinstr region

Borislav Petkov
2021-11-04T14:41:11Z

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, drop noinstr tracking around mce_log().

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>
---
arch/x86/kernel/cpu/mce/core.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index e31df79f87c7..961f80a4bd6f 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1175,13 +1175,14 @@ 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);
@@ -1208,7 +1209,7 @@ 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);

@@ -1231,7 +1232,9 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
/* assuming valid severity level != 0 */
m->severity = severity;

+ instrumentation_begin();
mce_log(m);
+ instrumentation_end();

if (severity > *worst) {
*final = *m;
@@ -1241,6 +1244,8 @@ 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)
@@ -1349,7 +1354,7 @@ 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;
@@ -1428,7 +1433,7 @@ 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);
@@ -1460,11 +1465,14 @@ noinstr void do_machine_check(struct pt_regs *regs)
}
}

+ instrumentation_begin();
+
+ if (taint)
+ add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+
if (worst != MCE_AR_SEVERITY && !kill_current_task)
goto out;

- instrumentation_begin();
-
/* 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. */
@@ -1494,9 +1502,9 @@ 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);
--
2.29.2