arm64/boot: Disable trapping of PMZR_EL0 writes to EL2grafted

__init_el2_fgt2() writes one mask to both HDFGRTR2_EL2 and HDFGWTR2_EL2.
PMZR_EL0 is write-only, so its trap bit, nPMZR_EL0, exists only in
HDFGWTR2_EL2 and is therefore never set: a PMZR_EL0 write from the host
traps to EL2, where the nVHE hypervisor has no handler and BUG()s. The
kernel never writes PMZR_EL0, but kernel.perf_user_access=1 has the PMU
driver set PMUSERENR_EL0.UEN for a task with a user-read event, so a
write from EL0 reaches the trap and takes the host down without a panic
message.

Accumulate the HDFGWTR2_EL2 bits separately, as __init_el2_fgt() already
does for HDFGWTR_EL2, and set nPMZR_EL0 with the other FEAT_PMUv3p9
bits.

Fixes: 858c7bfcb35e1 ("arm64/boot: Enable EL2 requirements for FEAT_PMUv3p9")
Cc: stable@vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 52 insertions, 0 deletions

diff --git a/include/vdso/futex.h b/include/vdso/futex.h
new file mode 100644
index 000000000..3cd175eef
--- /dev/null
+++ b/include/vdso/futex.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _VDSO_FUTEX_H
+#define _VDSO_FUTEX_H
+
+#include <uapi/linux/types.h>
+
+/**
+ * __vdso_futex_robust_list64_try_unlock - Try to unlock an uncontended robust futex
+ *					   with a 64-bit pending op pointer
+ * @lock:	Pointer to the futex lock object
+ * @tid:	The TID of the calling task
+ * @pop:	Pointer to the task's robust_list_head::list_pending_op
+ *
+ * Return: The content of *@lock. On success this is the same as @tid.
+ *
+ * The function implements:
+ *	if (atomic_try_cmpxchg(lock, &tid, 0))
+ *		*op = NULL;
+ *	return tid;
+ *
+ * There is a race between a successful unlock and clearing the pending op
+ * pointer in the robust list head. If the calling task is interrupted in the
+ * race window and has to handle a (fatal) signal on return to user space then
+ * the kernel handles the clearing of @pending_op before attempting to deliver
+ * the signal. That ensures that a task cannot exit with a potentially invalid
+ * pending op pointer.
+ *
+ * User space uses it in the following way:
+ *
+ * if (__vdso_futex_robust_list64_try_unlock(lock, tid, &pending_op) != tid)
+ *	err = sys_futex($OP | FUTEX_ROBUST_UNLOCK,....);
+ *
+ * If the unlock attempt fails due to the FUTEX_WAITERS bit set in the lock,
+ * then the syscall does the unlock, clears the pending op pointer and wakes the
+ * requested number of waiters.
+ */
+__u32 __vdso_futex_robust_list64_try_unlock(__u32 *lock, __u32 tid, __u64 *pop);
+
+/**
+ * __vdso_futex_robust_list32_try_unlock - Try to unlock an uncontended robust futex
+ *					   with a 32-bit pending op pointer
+ * @lock:	Pointer to the futex lock object
+ * @tid:	The TID of the calling task
+ * @pop:	Pointer to the task's robust_list_head::list_pending_op
+ *
+ * Return: The content of *@lock. On success this is the same as @tid.
+ *
+ * Same as __vdso_futex_robust_list64_try_unlock() just with a 32-bit @pop pointer.
+ */
+__u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop);
+
+#endif