openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 151 insertions, 0 deletions

diff --git a/security/landlock/access.h b/security/landlock/access.h
new file mode 100644
index 000000000..d926078bf
--- /dev/null
+++ b/security/landlock/access.h
@@ -0,0 +1,151 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock - Access types and helpers
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ * Copyright © 2024-2025 Microsoft Corporation
+ */
+
+#ifndef _SECURITY_LANDLOCK_ACCESS_H
+#define _SECURITY_LANDLOCK_ACCESS_H
+
+#include <linux/bitops.h>
+#include <linux/build_bug.h>
+#include <linux/kernel.h>
+#include <uapi/linux/landlock.h>
+
+#include "limits.h"
+
+/*
+ * All access rights that are denied by default whether they are handled or not
+ * by a ruleset/layer.  This must be ORed with all ruleset->access_masks[]
+ * entries when we need to get the absolute handled access masks, see
+ * landlock_upgrade_handled_access_masks().
+ */
+/* clang-format off */
+#define _LANDLOCK_ACCESS_FS_INITIALLY_DENIED ( \
+	LANDLOCK_ACCESS_FS_REFER)
+/* clang-format on */
+
+/* clang-format off */
+#define _LANDLOCK_ACCESS_FS_OPTIONAL ( \
+	LANDLOCK_ACCESS_FS_TRUNCATE | \
+	LANDLOCK_ACCESS_FS_IOCTL_DEV)
+/* clang-format on */
+
+typedef u32 access_mask_t;
+
+/* Makes sure all filesystem access rights can be stored. */
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
+/* Makes sure all network access rights can be stored. */
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_NET);
+/* Makes sure all scoped rights can be stored. */
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
+/* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
+static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
+
+/* Ruleset access masks. */
+struct access_masks {
+	access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
+	access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
+	access_mask_t scope : LANDLOCK_NUM_SCOPE;
+} __packed __aligned(sizeof(u32));
+
+union access_masks_all {
+	struct access_masks masks;
+	u32 all;
+};
+
+/* Makes sure all fields are covered. */
+static_assert(sizeof(typeof_member(union access_masks_all, masks)) ==
+	      sizeof(typeof_member(union access_masks_all, all)));
+
+/**
+ * struct layer_mask - The access rights and rule flags for a layer.
+ *
+ * This has a bit for each access rights and rule flags.  During access checks,
+ * it is used to represent the access rights for each layer which still need to
+ * be fulfilled.  When all bits are 0, the access request is considered to be
+ * fulfilled.
+ */
+struct layer_mask {
+	/**
+	 * @access: The unfulfilled access rights for this layer.
+	 */
+	access_mask_t access : LANDLOCK_NUM_ACCESS_MAX;
+#ifdef CONFIG_AUDIT
+	/**
+	 * @quiet: Whether we have encountered a rule with the quiet flag for
+	 * this layer.  Used to control logging.
+	 */
+	access_mask_t quiet : 1;
+#endif /* CONFIG_AUDIT */
+} __packed __aligned(sizeof(access_mask_t));
+
+/*
+ * Make sure that we don't increase the size of struct layer_mask when storing
+ * rule flags.
+ */
+static_assert(sizeof(struct layer_mask) == sizeof(access_mask_t));
+
+/**
+ * struct layer_masks - An array of struct layer_mask, one per layer.
+ */
+struct layer_masks {
+	/**
+	 * @layers: The unfulfilled access rights for each layer.
+	 */
+	struct layer_mask layers[LANDLOCK_MAX_NUM_LAYERS];
+};
+
+/*
+ * Tracks domains responsible of a denied access.  This avoids storing in each
+ * object the full matrix of per-layer unfulfilled access rights, which is
+ * required by update_request().
+ *
+ * Each nibble represents the layer index of the newest layer which denied a
+ * certain access right.  For file system access rights, the upper four bits are
+ * the index of the layer which denies LANDLOCK_ACCESS_FS_IOCTL_DEV and the
+ * lower nibble represents LANDLOCK_ACCESS_FS_TRUNCATE.
+ */
+typedef u8 deny_masks_t;
+
+/*
+ * Makes sure all optional access rights can be tied to a layer index (cf.
+ * get_deny_mask).
+ */
+static_assert(BITS_PER_TYPE(deny_masks_t) >=
+	      (HWEIGHT(LANDLOCK_MAX_NUM_LAYERS - 1) *
+	       HWEIGHT(_LANDLOCK_ACCESS_FS_OPTIONAL)));
+
+/* LANDLOCK_MAX_NUM_LAYERS must be a power of two (cf. deny_masks_t assert). */
+static_assert(HWEIGHT(LANDLOCK_MAX_NUM_LAYERS) == 1);
+
+/* Upgrades with all initially denied by default access rights. */
+static inline struct access_masks
+landlock_upgrade_handled_access_masks(struct access_masks access_masks)
+{
+	/*
+	 * All access rights that are denied by default whether they are
+	 * explicitly handled or not.
+	 */
+	if (access_masks.fs)
+		access_masks.fs |= _LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
+
+	return access_masks;
+}
+
+/* Checks the subset relation between access masks. */
+static inline bool access_mask_subset(access_mask_t subset,
+				      access_mask_t superset)
+{
+	return (subset | superset) == superset;
+}
+
+/* A bitmask that is large enough to hold set of optional accesses. */
+typedef u8 optional_access_t;
+static_assert(BITS_PER_TYPE(optional_access_t) >=
+	      HWEIGHT(_LANDLOCK_ACCESS_FS_OPTIONAL));
+
+#endif /* _SECURITY_LANDLOCK_ACCESS_H */