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, 202 insertions, 0 deletions

diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
new file mode 100644
index 000000000..5977723fb
--- /dev/null
+++ b/include/vdso/datapage.h
@@ -0,0 +1,202 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_DATAPAGE_H
+#define __VDSO_DATAPAGE_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+
+#include <uapi/linux/bits.h>
+#include <uapi/linux/time.h>
+
+#include <vdso/align.h>
+#include <vdso/bits.h>
+#include <vdso/cache.h>
+#include <vdso/page.h>
+#include <vdso/time.h>
+
+#ifdef CONFIG_ARCH_HAS_VDSO_TIME_DATA
+#include <asm/vdso/time_data.h>
+#else
+struct arch_vdso_time_data {};
+#endif
+
+#if defined(CONFIG_ARCH_HAS_VDSO_ARCH_DATA)
+#include <asm/vdso/arch_data.h>
+#else
+struct vdso_arch_data {
+	/* Needed for the generic code, never actually used at runtime */
+	char __unused;
+};
+#endif
+
+#define VDSO_BASES	(CLOCK_TAI + 1)
+#define VDSO_BASE_AUX	0
+#define VDSO_HRES	(BIT(CLOCK_REALTIME)		| \
+			 BIT(CLOCK_MONOTONIC)		| \
+			 BIT(CLOCK_BOOTTIME)		| \
+			 BIT(CLOCK_TAI))
+#define VDSO_COARSE	(BIT(CLOCK_REALTIME_COARSE)	| \
+			 BIT(CLOCK_MONOTONIC_COARSE))
+#define VDSO_RAW	(BIT(CLOCK_MONOTONIC_RAW))
+#define VDSO_AUX	__GENMASK(CLOCK_AUX_LAST, CLOCK_AUX)
+
+#define CS_HRES_COARSE	0
+#define CS_RAW		1
+#define CS_BASES	(CS_RAW + 1)
+
+/**
+ * struct vdso_timestamp - basetime per clock_id
+ * @sec:	seconds
+ * @nsec:	nanoseconds
+ *
+ * There is one vdso_timestamp object in vvar for each vDSO-accelerated
+ * clock_id. For high-resolution clocks, this encodes the time
+ * corresponding to vdso_time_data.cycle_last. For coarse clocks this encodes
+ * the actual time.
+ *
+ * To be noticed that for highres clocks nsec is left-shifted by
+ * vdso_time_data[x].shift.
+ */
+struct vdso_timestamp {
+	u64	sec;
+	u64	nsec;
+};
+
+/**
+ * struct vdso_clock - vdso per clocksource datapage representation
+ * @seq:		timebase sequence counter
+ * @clock_mode:		clock mode
+ * @cycle_last:		timebase at clocksource init
+ * @max_cycles:		maximum cycles which won't overflow 64bit multiplication
+ * @mask:		clocksource mask
+ * @mult:		clocksource multiplier
+ * @shift:		clocksource shift
+ * @basetime:		basetime per clock_id
+ * @offset:		time namespace offset per clock_id
+ *
+ * See also struct vdso_time_data for basic access and ordering information as
+ * struct vdso_clock is used there.
+ *
+ * @basetime is used to store the base time for the system wide time getter
+ * VVAR page.
+ *
+ * @offset is used by the special time namespace VVAR pages which are
+ * installed instead of the real VVAR page. These namespace pages must set
+ * @seq to 1 and @clock_mode to VDSO_CLOCKMODE_TIMENS to force the code into
+ * the time namespace slow path. The namespace aware functions retrieve the
+ * real system wide VVAR page, read host time and add the per clock offset.
+ * For clocks which are not affected by time namespace adjustment the
+ * offset must be zero.
+ */
+struct vdso_clock {
+	u32			seq;
+
+	s32			clock_mode;
+	u64			cycle_last;
+#ifdef CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT
+	u64			max_cycles;
+#endif
+	u64			mask;
+	u32			mult;
+	u32			shift;
+
+	union {
+		struct vdso_timestamp	basetime[VDSO_BASES];
+		struct timens_offset	offset[VDSO_BASES];
+	};
+};
+
+/**
+ * struct vdso_time_data - vdso datapage representation
+ * @arch_data:		architecture specific data (optional, defaults
+ *			to an empty struct)
+ * @clock_data:		clocksource related data (array)
+ * @aux_clock_data:	auxiliary clocksource related data (array)
+ * @tz_minuteswest:	minutes west of Greenwich
+ * @tz_dsttime:		type of DST correction
+ * @hrtimer_res:	hrtimer resolution
+ * @__unused:		unused
+ *
+ * vdso_time_data will be accessed by 64 bit and compat code at the same time
+ * so we should be careful before modifying this structure.
+ *
+ * The ordering of the struct members is optimized to have fast acces to the
+ * often required struct members which are related to CLOCK_REALTIME and
+ * CLOCK_MONOTONIC. This information is stored in the first cache lines.
+ */
+struct vdso_time_data {
+	struct arch_vdso_time_data	arch_data;
+
+	struct vdso_clock		clock_data[CS_BASES];
+	struct vdso_clock		aux_clock_data[MAX_AUX_CLOCKS];
+
+	s32				tz_minuteswest;
+	s32				tz_dsttime;
+	u32				hrtimer_res;
+	u32				__unused;
+} ____cacheline_aligned;
+
+/**
+ * struct vdso_rng_data - vdso RNG state information
+ * @generation:	counter representing the number of RNG reseeds
+ * @is_ready:	boolean signaling whether the RNG is initialized
+ */
+struct vdso_rng_data {
+	u64	generation;
+	u8	is_ready;
+};
+
+/*
+ * We use the hidden visibility to prevent the compiler from generating a GOT
+ * relocation. Not only is going through a GOT useless (the entry couldn't and
+ * must not be overridden by another library), it does not even work: the linker
+ * cannot generate an absolute address to the data page.
+ *
+ * With the hidden visibility, the compiler simply generates a PC-relative
+ * relocation, and this is what we need.
+ */
+extern struct vdso_time_data vdso_u_time_data __attribute__((visibility("hidden")));
+extern struct vdso_rng_data vdso_u_rng_data __attribute__((visibility("hidden")));
+extern struct vdso_arch_data vdso_u_arch_data __attribute__((visibility("hidden")));
+
+extern struct vdso_time_data *vdso_k_time_data;
+extern struct vdso_rng_data *vdso_k_rng_data;
+extern struct vdso_arch_data *vdso_k_arch_data;
+
+#define VDSO_ARCH_DATA_SIZE ALIGN(sizeof(struct vdso_arch_data), PAGE_SIZE)
+#define VDSO_ARCH_DATA_PAGES (VDSO_ARCH_DATA_SIZE >> PAGE_SHIFT)
+
+enum vdso_pages {
+	VDSO_TIME_PAGE_OFFSET,
+	VDSO_TIMENS_PAGE_OFFSET,
+	VDSO_RNG_PAGE_OFFSET,
+	VDSO_ARCH_PAGES_START,
+	VDSO_ARCH_PAGES_END = VDSO_ARCH_PAGES_START + VDSO_ARCH_DATA_PAGES - 1,
+	VDSO_NR_PAGES
+};
+
+#else /* !__ASSEMBLY__ */
+
+#ifdef CONFIG_VDSO_GETRANDOM
+#define __vdso_u_rng_data	PROVIDE(vdso_u_rng_data = vdso_u_data + 2 * PAGE_SIZE);
+#else
+#define __vdso_u_rng_data
+#endif
+
+#ifdef CONFIG_ARCH_HAS_VDSO_ARCH_DATA
+#define __vdso_u_arch_data	PROVIDE(vdso_u_arch_data = vdso_u_data + 3 * PAGE_SIZE);
+#else
+#define __vdso_u_arch_data
+#endif
+
+#define VDSO_VVAR_SYMS						\
+	PROVIDE(vdso_u_data = . - __VDSO_PAGES * PAGE_SIZE);	\
+	PROVIDE(vdso_u_time_data = vdso_u_data);		\
+	__vdso_u_rng_data					\
+	__vdso_u_arch_data					\
+
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __VDSO_DATAPAGE_H */