[PATCH v12 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

[Shuai Xue]

Synchronous error was detected as a result of user-space process accessing
a 2-bit uncorrected error. The CPU will take a synchronous error exception
such as Synchronous External Abort (SEA) on Arm64. The kernel will queue a
memory_failure() work which poisons the related page, unmaps the page, and
then sends a SIGBUS to the process, so that a system wide panic can be
avoided.

However, no memory_failure() work will be queued unless all bellow
preconditions check passed:

- `if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))` in ghes_handle_memory_failure()
- `if (flags == -1)` in ghes_handle_memory_failure()
- `if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))` in ghes_do_memory_failure()
- `if (!pfn_valid(pfn) && !arch_is_platform_page(physical_addr)) ` in ghes_do_memory_failure()

In such case, the user-space process will trigger SEA again.  This loop
can potentially exceed the platform firmware threshold or even trigger a
kernel hard lockup, leading to a system reboot.

Fix it by performing a force kill if no memory_failure() work is queued
for synchronous errors.

Suggested-by: Xiaofei Tan <tanxiaofei@xxxxxxxxxx>
Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>

---
 drivers/acpi/apei/ghes.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 623cc0cb4a65..b0b20ee533d9 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -801,6 +801,16 @@ static bool ghes_do_proc(struct ghes *ghes,
 		}
 	}
 
+	/*
+	 * If no memory failure work is queued for abnormal synchronous
+	 * errors, do a force kill.
+	 */
+	if (sync && !queued) {
+		pr_err("Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+			current->comm, task_pid_nr(current));
+		force_sig(SIGBUS);
+	}
+
 	return queued;
 }
 
-- 
2.39.3