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SubjectRe: [PATCH v19 04/15] mm: untag user pointers passed to memory syscalls
On Tue, Jul 23, 2019 at 07:58:41PM +0200, Andrey Konovalov wrote:
> 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.
>
> This patch allows tagged pointers to be passed to the following memory
> syscalls: get_mempolicy, madvise, mbind, mincore, mlock, mlock2, mprotect,
> mremap, msync, munlock, move_pages.
>
> The mmap and mremap syscalls do not currently accept tagged addresses.
> Architectures may interpret the tag as a background colour for the
> corresponding vma.
>
> Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
> mm/madvise.c | 2 ++
> mm/mempolicy.c | 3 +++
> mm/migrate.c | 2 +-
> mm/mincore.c | 2 ++
> mm/mlock.c | 4 ++++
> mm/mprotect.c | 2 ++
> mm/mremap.c | 7 +++++++
> mm/msync.c | 2 ++
> 8 files changed, 23 insertions(+), 1 deletion(-)

More back and forth discussions on how to specify the exceptions here.
I'm proposing just dropping the exceptions and folding in the diff
below.

Andrew, if you prefer a standalone patch instead, please let me know:

------------------8<----------------------------
From 9a5286acaa638c6a917d96986bf28dad35e24a0c Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Fri, 9 Aug 2019 14:21:33 +0100
Subject: [PATCH] fixup! mm: untag user pointers passed to memory syscalls

mmap, mremap, munmap, brk added to the list of syscalls that accept
tagged pointers.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
mm/mmap.c | 5 +++++
mm/mremap.c | 6 +-----
2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 7e8c3e8ae75f..b766b633b7ae 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -201,6 +201,8 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
bool downgraded = false;
LIST_HEAD(uf);

+ brk = untagged_addr(brk);
+
if (down_write_killable(&mm->mmap_sem))
return -EINTR;

@@ -1573,6 +1575,8 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
struct file *file = NULL;
unsigned long retval;

+ addr = untagged_addr(addr);
+
if (!(flags & MAP_ANONYMOUS)) {
audit_mmap_fd(fd, flags);
file = fget(fd);
@@ -2874,6 +2878,7 @@ EXPORT_SYMBOL(vm_munmap);

SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
+ addr = untagged_addr(addr);
profile_munmap(addr);
return __vm_munmap(addr, len, true);
}
diff --git a/mm/mremap.c b/mm/mremap.c
index 64c9a3b8be0a..1fc8a29fbe3f 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -606,12 +606,8 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
LIST_HEAD(uf_unmap_early);
LIST_HEAD(uf_unmap);

- /*
- * Architectures may interpret the tag passed to mmap as a background
- * colour for the corresponding vma. For mremap we don't allow tagged
- * new_addr to preserve similar behaviour to mmap.
- */
addr = untagged_addr(addr);
+ new_addr = untagged_addr(new_addr);

if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
return ret;
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