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Subject[PATCH v4 00/10] prevent bounds-check bypass via speculative execution
Changes since v3 [1]
* Drop 'ifence_array_ptr' and associated compile-time + run-time
switching and just use the masking approach all the time.

* Convert 'get_user' to use pointer sanitization via masking rather than
lfence. '__get_user' and associated paths still rely on
lfence. (Linus)

"Basically, the rule is trivial: find all 'stac' users, and use
address masking if those users already integrate the limit
check, and lfence they don't."

* At syscall entry sanitize the syscall number under speculation
to remove a user controlled pointer de-reference in kernel
space. (Linus)

* Fix a raw lfence in the kvm code (added for v4.15-rc8) to use

* Propose 'array_idx' as a way to sanitize user input that is
later used as an array index, but where the validation is
happening in a different code block than the array reference.

* Fix grammar in speculation.txt (Kees)


Quoting Mark's original RFC:

"Recently, Google Project Zero discovered several classes of attack
against speculative execution. One of these, known as variant-1, allows
explicit bounds checks to be bypassed under speculation, providing an
arbitrary read gadget. Further details can be found on the GPZ blog [2]
and the Documentation patch in this series."

A precondition of using this attack on the kernel is to get a user
controlled pointer de-referenced (under speculation) in privileged code.
The primary source of user controlled pointers in the kernel is the
arguments passed to 'get_user' and '__get_user'. An example of other
user controlled pointers are user-controlled array / pointer offsets.

Better tooling is needed to find more arrays / pointers with user
controlled indices / offsets that can be converted to use 'array_ptr' or
'array_idx'. A few are included in this set, and these are not expected
to be complete. That said, the 'get_user' protections raise the bar on
finding a vulnerable gadget in the kernel.

These patches are also available via the 'nospec-v4' git branch here:

git:// nospec-v4

Note that the BPF fix for Spectre variant1 is merged for 4.15-rc8.



Dan Williams (9):
asm/nospec, array_ptr: sanitize speculative array de-references
x86: implement array_ptr_mask()
x86: introduce __uaccess_begin_nospec and ifence
x86, __get_user: use __uaccess_begin_nospec
x86, get_user: use pointer masking to limit speculation
x86: narrow out of bounds syscalls to sys_read under speculation
vfs, fdtable: prevent bounds-check bypass via speculative execution
kvm, x86: fix spectre-v1 mitigation
nl80211: sanitize array index in parse_txq_params

Mark Rutland (1):
Documentation: document array_ptr

Documentation/speculation.txt | 143 +++++++++++++++++++++++++++++++++++++
arch/x86/entry/entry_64.S | 2 +
arch/x86/include/asm/barrier.h | 28 +++++++
arch/x86/include/asm/msr.h | 3 -
arch/x86/include/asm/smap.h | 24 ++++++
arch/x86/include/asm/uaccess.h | 15 +++-
arch/x86/include/asm/uaccess_32.h | 6 +-
arch/x86/include/asm/uaccess_64.h | 12 ++-
arch/x86/kvm/vmx.c | 19 ++---
arch/x86/lib/getuser.S | 5 +
arch/x86/lib/usercopy_32.c | 8 +-
include/linux/fdtable.h | 7 +-
include/linux/nospec.h | 65 +++++++++++++++++
net/wireless/nl80211.c | 10 ++-
14 files changed, 312 insertions(+), 35 deletions(-)
create mode 100644 Documentation/speculation.txt
create mode 100644 include/linux/nospec.h

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