ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 28 insertions, 0 deletions

diff --git a/tools/perf/util/sample-raw.c b/tools/perf/util/sample-raw.c
new file mode 100644
index 000000000..e20b73c0c
--- /dev/null
+++ b/tools/perf/util/sample-raw.c
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include "sample-raw.h"
+
+#include <elf.h>
+#include <linux/string.h>
+
+#include "env.h"
+#include "evlist.h"
+#include "header.h"
+#include "session.h"
+
+/*
+ * Check platform the perf data file was created on and perform platform
+ * specific interpretation.
+ */
+void evlist__init_trace_event_sample_raw(struct evlist *evlist, struct perf_env *env)
+{
+	uint16_t e_machine = perf_env__e_machine(env, /*e_flags=*/NULL);
+
+	if (e_machine == EM_S390) {
+		evlist->trace_event_sample_raw = evlist__s390_sample_raw;
+	} else if (e_machine == EM_X86_64 || e_machine == EM_386) {
+		const char *cpuid = perf_env__cpuid(env);
+
+		if (cpuid && strstarts(cpuid, "AuthenticAMD") && evlist__has_amd_ibs(evlist))
+			evlist->trace_event_sample_raw = evlist__amd_sample_raw;
+	}
+}