Kalesh Singh
f350c4c66c
SPF attempts page faults without taking the mmap lock, but takes the
PTL. If there is a concurrent fast mremap (at PMD/PUD level), this
can lead to a UAF as fast mremap will only take the PTL locks at the
PMD/PUD level. SPF cannot take the PTL locks at the larger subtree
granularity since this introduces much contention in the page fault
paths.
To address the race:
1) Only try fast mremaps if there are no users of the VMA. Android
is concerned with this optimization in the context of
GC stop-the-world pause. So there are no other threads active
and this should almost always succeed.
2) Speculative faults detect ongoing fast mremaps and fallback
to conventional fault handling (taking mmap read lock).
Bug: 263177905
Change-Id: I23917e493ddc8576de19883cac053dfde9982b7f
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Git-commit: 529351c4c8202aa7f5bc4a8a100e583a70ab6110
Git-repo: https://android.googlesource.com/kernel/common/
[quic_c_spathi@quicinc.com: resolve merge conflicts. Not applying
mremap changes due to absence of applicable configs for race.]
Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.