[RFC PATCH v1 2/2] arm64/mm: use VMA lock for kernel faults on user addresses

["Barry Song (Xiaomi)" <baohua@kernel.org>]

Use the VMA lock for kernel faults on user addresses. This also
makes the existing code below meaningful:

/* Quick path to respond to signals */
if (fault_signal_pending(fault, regs)) {
	if (!user_mode(regs))
		goto no_context;
	return 0;
}

Right now, the code above is dead because !user_mode always
takes the mmap_lock path.

Co-developed-by: Bo Zhang <zhangbo56@xiaomi.com>
Signed-off-by: Bo Zhang <zhangbo56@xiaomi.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 arch/arm64/mm/fault.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 85e23388f9bb..241f1ab07ab3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -607,6 +607,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 	unsigned int mm_flags = FAULT_FLAG_DEFAULT;
 	unsigned long addr = untagged_addr(far);
 	struct vm_area_struct *vma;
+	bool uaccess = false;
 	int si_code;
 	int pkey = -1;
 
@@ -663,6 +664,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 		if (!insn_may_access_user(regs->pc, esr))
 			die_kernel_fault("access to user memory outside uaccess routines",
 					 addr, esr, regs);
+		uaccess = true;
 	}
 
 	if (is_pkvm_stage2_abort(esr)) {
@@ -674,7 +676,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 
-	if (!(mm_flags & FAULT_FLAG_USER))
+	if (!(mm_flags & FAULT_FLAG_USER) && !uaccess)
 		goto lock_mmap;
 
 	vma = lock_vma_under_rcu(mm, addr);
-- 
2.39.3 (Apple Git-146)