Thread (27 messages) 27 messages, 5 authors, 2019-03-18
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[PATCH v11 05/14] mm, arm64: untag user pointers in mm/gup.c

From: Andrey Konovalov <hidden>
Date: 2019-03-15 19:52:04
Also in: bpf, linux-arch, linux-arm-kernel, linux-doc, linux-kselftest, linux-mm, lkml
Subsystem: memory management, memory management - gup (get user pages), the rest · Maintainers: Andrew Morton, David Hildenbrand, Linus Torvalds

This patch is a part of a series that extends arm64 kernel ABI to allow to
pass tagged user pointers (with the top byte set to something else other
than 0x00) as syscall arguments.

mm/gup.c provides a kernel interface that accepts user addresses and
manipulates user pages directly (for example get_user_pages, that is used
by the futex syscall). Since a user can provided tagged addresses, we need
to handle this case.

Add untagging to gup.c functions that use user addresses for vma lookups.

Signed-off-by: Andrey Konovalov <redacted>
---
 mm/gup.c | 4 ++++
 1 file changed, 4 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c
index f84e22685aaa..3192741e0b3a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -686,6 +686,8 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 	if (!nr_pages)
 		return 0;
 
+	start = untagged_addr(start);
+
 	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
 
 	/*
@@ -848,6 +850,8 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 	struct vm_area_struct *vma;
 	vm_fault_t ret, major = 0;
 
+	address = untagged_addr(address);
+
 	if (unlocked)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 
-- 
2.21.0.360.g471c308f928-goog
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