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mm: untag user pointers in mm/gup.c
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This patch is a part of a series that extends 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.

Link: http://lkml.kernel.org/r/4731bddba3c938658c10ff4ed55cc01c60f4c8f8.1563904656.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <[email protected]>
Reviewed-by: Khalid Aziz <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Eric Auger <[email protected]>
Cc: Felix Kuehling <[email protected]>
Cc: Jens Wiklander <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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xairy authored and torvalds committed Sep 26, 2019
1 parent 057d338 commit f965259
Showing 1 changed file with 4 additions and 0 deletions.
4 changes: 4 additions & 0 deletions mm/gup.c
Original file line number Diff line number Diff line change
Expand Up @@ -788,6 +788,8 @@ 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));

/*
Expand Down Expand Up @@ -950,6 +952,8 @@ 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;

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