mm: Avoid creating virtual address aliases in brk()/mmap()/mremap() (dcde2373) · Commits · 戴 / test

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 ("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: ("mm: untag user pointers in mmap/munmap/mremap/brk") Cc: <stable@vger.kernel.org> # 5.4.x- Cc: Florian Weimer <fweimer@redhat.com> Reviewed-by:

Andrew Morton <akpm@linux-foundation.org> 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> Signed-off-by:

Will Deacon <will@kernel.org>

Documentation/arm64/tagged-address-abi.rst

+9 −2

Original line number	Diff line number	Diff line
		@@ -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 to alias 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

mm/mmap.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -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;

		@@ -1557,8 +1555,6 @@ 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);

mm/mremap.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -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;

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