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-rw-r--r--0001-mm-Avoid-creating-virtual-address-aliases-in-brk-mma.patch95
1 files changed, 95 insertions, 0 deletions
diff --git a/0001-mm-Avoid-creating-virtual-address-aliases-in-brk-mma.patch b/0001-mm-Avoid-creating-virtual-address-aliases-in-brk-mma.patch
new file mode 100644
index 000000000..6f3bd3c72
--- /dev/null
+++ b/0001-mm-Avoid-creating-virtual-address-aliases-in-brk-mma.patch
@@ -0,0 +1,95 @@
+From a34309d16f41c48ffd90e56a6f865d6a1a8c49f0 Mon Sep 17 00:00:00 2001
+From: Catalin Marinas <catalin.marinas@arm.com>
+Date: Wed, 19 Feb 2020 12:31:56 +0000
+Subject: [PATCH] mm: Avoid creating virtual address aliases in
+ brk()/mmap()/mremap()
+
+Currently the arm64 kernel ignores the top address byte passed to brk(),
+mmap() and mremap(). When the user is not aware of the 56-bit address
+limit or relies on the kernel to return an error, untagging such
+pointers has the potential to create address aliases in user-space.
+Passing a tagged address to munmap(), madvise() is permitted since the
+tagged pointer is expected to be inside an existing mapping.
+
+The current behaviour breaks the existing glibc malloc() implementation
+which relies on brk() with an address beyond 56-bit to be rejected by
+the kernel.
+
+Remove untagging in the above functions by partially reverting commit
+ce18d171cb73 ("mm: untag user pointers in mmap/munmap/mremap/brk"). In
+addition, update the arm64 tagged-address-abi.rst document accordingly.
+
+Link: https://bugzilla.redhat.com/1797052
+Fixes: ce18d171cb73 ("mm: untag user pointers in mmap/munmap/mremap/brk")
+Cc: <stable@vger.kernel.org> # 5.4.x-
+Cc: Andrew Morton <akpm@linux-foundation.org>
+Cc: Florian Weimer <fweimer@redhat.com>
+Reported-by: Victor Stinner <vstinner@redhat.com>
+Acked-by: Will Deacon <will@kernel.org>
+Acked-by: Andrey Konovalov <andreyknvl@google.com>
+Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
+---
+ Documentation/arm64/tagged-address-abi.rst | 11 +++++++++--
+ mm/mmap.c | 4 ----
+ mm/mremap.c | 1 -
+ 3 files changed, 9 insertions(+), 7 deletions(-)
+
+diff --git a/Documentation/arm64/tagged-address-abi.rst b/Documentation/arm64/tagged-address-abi.rst
+index d4a85d535bf9..f6289116893c 100644
+--- a/Documentation/arm64/tagged-address-abi.rst
++++ b/Documentation/arm64/tagged-address-abi.rst
+@@ -44,8 +44,15 @@ The AArch64 Tagged Address ABI has two stages of relaxation depending
+ how the user addresses are used by the kernel:
+
+ 1. User addresses not accessed by the kernel but used for address space
+- management (e.g. ``mmap()``, ``mprotect()``, ``madvise()``). The use
+- of valid tagged pointers in this context is always allowed.
++ management (e.g. ``mprotect()``, ``madvise()``). The use of valid
++ tagged pointers in this context is allowed with the exception of
++ ``brk()``, ``mmap()`` and the ``new_address`` argument to
++ ``mremap()`` as these have the potential of aliasing with existing
++ user addresses.
++
++ NOTE: This behaviour changed in v5.6 and so some earlier kernels may
++ incorrectly accept valid tagged pointers for the ``brk()``,
++ ``mmap()`` and ``mremap()`` system calls.
+
+ 2. User addresses accessed by the kernel (e.g. ``write()``). This ABI
+ relaxation is disabled by default and the application thread needs to
+diff --git a/mm/mmap.c b/mm/mmap.c
+index 4390dbea4aa5..514cc19c5916 100644
+--- a/mm/mmap.c
++++ b/mm/mmap.c
+@@ -195,8 +195,6 @@ 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;
+
+@@ -1583,8 +1581,6 @@ 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);
+diff --git a/mm/mremap.c b/mm/mremap.c
+index 1fc8a29fbe3f..1d98281f7204 100644
+--- a/mm/mremap.c
++++ b/mm/mremap.c
+@@ -607,7 +607,6 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
+ LIST_HEAD(uf_unmap);
+
+ addr = untagged_addr(addr);
+- new_addr = untagged_addr(new_addr);
+
+ if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
+ return ret;
+--
+2.24.1
+