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, 157 insertions, 0 deletions

diff --git a/lib/raid/raid6/mktables.c b/lib/raid/raid6/mktables.c
new file mode 100644
index 000000000..b6327b562
--- /dev/null
+++ b/lib/raid/raid6/mktables.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2002-2007 H. Peter Anvin - All Rights Reserved
+ *
+ * Make RAID-6 tables.  This is a host user space program to be run at compile
+ * time.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <time.h>
+
+static uint8_t gfmul(uint8_t a, uint8_t b)
+{
+	uint8_t v = 0;
+
+	while (b) {
+		if (b & 1)
+			v ^= a;
+		a = (a << 1) ^ (a & 0x80 ? 0x1d : 0);
+		b >>= 1;
+	}
+
+	return v;
+}
+
+static uint8_t gfpow(uint8_t a, int b)
+{
+	uint8_t v = 1;
+
+	b %= 255;
+	if (b < 0)
+		b += 255;
+
+	while (b) {
+		if (b & 1)
+			v = gfmul(v, a);
+		a = gfmul(a, a);
+		b >>= 1;
+	}
+
+	return v;
+}
+
+int main(int argc, char *argv[])
+{
+	int i, j, k;
+	uint8_t v;
+	uint8_t exptbl[256], invtbl[256];
+
+	printf("#include <linux/export.h>\n");
+	printf("#include \"algos.h\"\n");
+
+	/* Compute multiplication table */
+	printf("\nconst u8  __attribute__((aligned(256)))\n"
+		"raid6_gfmul[256][256] =\n"
+		"{\n");
+	for (i = 0; i < 256; i++) {
+		printf("\t{\n");
+		for (j = 0; j < 256; j += 8) {
+			printf("\t\t");
+			for (k = 0; k < 8; k++)
+				printf("0x%02x,%c", gfmul(i, j + k),
+				       (k == 7) ? '\n' : ' ');
+		}
+		printf("\t},\n");
+	}
+	printf("};\n");
+	printf("EXPORT_SYMBOL(raid6_gfmul);\n");
+
+	/* Compute vector multiplication table */
+	printf("\nconst u8  __attribute__((aligned(256)))\n"
+		"raid6_vgfmul[256][32] =\n"
+		"{\n");
+	for (i = 0; i < 256; i++) {
+		printf("\t{\n");
+		for (j = 0; j < 16; j += 8) {
+			printf("\t\t");
+			for (k = 0; k < 8; k++)
+				printf("0x%02x,%c", gfmul(i, j + k),
+				       (k == 7) ? '\n' : ' ');
+		}
+		for (j = 0; j < 16; j += 8) {
+			printf("\t\t");
+			for (k = 0; k < 8; k++)
+				printf("0x%02x,%c", gfmul(i, (j + k) << 4),
+				       (k == 7) ? '\n' : ' ');
+		}
+		printf("\t},\n");
+	}
+	printf("};\n");
+	printf("EXPORT_SYMBOL(raid6_vgfmul);\n");
+
+	/* Compute power-of-2 table (exponent) */
+	v = 1;
+	printf("\nconst u8 __attribute__((aligned(256)))\n"
+	       "raid6_gfexp[256] =\n" "{\n");
+	for (i = 0; i < 256; i += 8) {
+		printf("\t");
+		for (j = 0; j < 8; j++) {
+			exptbl[i + j] = v;
+			printf("0x%02x,%c", v, (j == 7) ? '\n' : ' ');
+			v = gfmul(v, 2);
+			if (v == 1)
+				v = 0;	/* For entry 255, not a real entry */
+		}
+	}
+	printf("};\n");
+	printf("EXPORT_SYMBOL(raid6_gfexp);\n");
+
+	/* Compute log-of-2 table */
+	printf("\nconst u8 __attribute__((aligned(256)))\n"
+	       "raid6_gflog[256] =\n" "{\n");
+	for (i = 0; i < 256; i += 8) {
+		printf("\t");
+		for (j = 0; j < 8; j++) {
+			v = 255;
+			for (k = 0; k < 256; k++)
+				if (exptbl[k] == (i + j)) {
+					v = k;
+					break;
+				}
+			printf("0x%02x,%c", v, (j == 7) ? '\n' : ' ');
+		}
+	}
+	printf("};\n");
+	printf("EXPORT_SYMBOL(raid6_gflog);\n");
+
+	/* Compute inverse table x^-1 == x^254 */
+	printf("\nconst u8 __attribute__((aligned(256)))\n"
+	       "raid6_gfinv[256] =\n" "{\n");
+	for (i = 0; i < 256; i += 8) {
+		printf("\t");
+		for (j = 0; j < 8; j++) {
+			invtbl[i + j] = v = gfpow(i + j, 254);
+			printf("0x%02x,%c", v, (j == 7) ? '\n' : ' ');
+		}
+	}
+	printf("};\n");
+	printf("EXPORT_SYMBOL(raid6_gfinv);\n");
+
+	/* Compute inv(2^x + 1) (exponent-xor-inverse) table */
+	printf("\nconst u8 __attribute__((aligned(256)))\n"
+	       "raid6_gfexi[256] =\n" "{\n");
+	for (i = 0; i < 256; i += 8) {
+		printf("\t");
+		for (j = 0; j < 8; j++)
+			printf("0x%02x,%c", invtbl[exptbl[i + j] ^ 1],
+			       (j == 7) ? '\n' : ' ');
+	}
+	printf("};\n");
+	printf("EXPORT_SYMBOL(raid6_gfexi);\n");
+
+	return 0;
+}