The GWP-ASan recoverable mode allows a process to continue to function
after a GWP-ASan error is detected. The error will continue to be
dumped, but GWP-ASan now has APIs that a signal handler (like the
example optional crash handler) can call in order to allow the
continuation of a process.
When an error occurs with an allocation, the slot used for that
allocation will be permanently disabled. This means that free() of that
pointer is a no-op, and use-after-frees will succeed (writing and
reading the data present in the page).
For heap-buffer-overflow/underflow, the guard page is marked as accessible
and buffer-overflows will succeed (writing and reading the data present
in the now-accessible guard page). This does impact adjacent
allocations, buffer-underflow and buffer-overflows from adjacent
allocations will no longer touch an inaccessible guard page. This could
be improved in future by having two guard pages between each adjacent
allocation, but that's out of scope of this patch.
Each allocation only ever has a single error report generated. It's
whatever came first between invalid-free, double-free, use-after-free or
heap-buffer-overflow, but only one.
Reviewed By: eugenis, fmayer
Differential Revision: https://reviews.llvm.org/D140173
The GWP-ASan recoverable mode allows a process to continue to function
after a GWP-ASan error is detected. The error will continue to be
dumped, but GWP-ASan now has APIs that a signal handler (like the
example optional crash handler) can call in order to allow the
continuation of a process.
When an error occurs with an allocation, the slot used for that
allocation will be permanently disabled. This means that free() of that
pointer is a no-op, and use-after-frees will succeed (writing and
reading the data present in the page).
For heap-buffer-overflow/underflow, the guard page is marked as accessible
and buffer-overflows will succeed (writing and reading the data present
in the now-accessible guard page). This does impact adjacent
allocations, buffer-underflow and buffer-overflows from adjacent
allocations will no longer touch an inaccessible guard page. This could
be improved in future by having two guard pages between each adjacent
allocation, but that's out of scope of this patch.
Each allocation only ever has a single error report generated. It's
whatever came first between invalid-free, double-free, use-after-free or
heap-buffer-overflow, but only one.
Reviewed By: eugenis, fmayer
Differential Revision: https://reviews.llvm.org/D140173
GWP-ASan's `AllocatorState` was recently extended with a
`AllocatorVersionMagic` structure required so that GWP-ASan bug reports
can be understood by tools at different versions.
On Fuchsia, this in included in the `scudo::Allocator` structure, and
by having non-zero initializers, this effectively moved the static
allocator structure from the `.bss` segment to the `.data` segment, thus
increasing (significantly) the size of the libc.
This CL proposes to initialize the structure with its magic numbers at
runtime, allowing for the allocator to go back into the `.bss` segment.
I will work on adding a test on the Scudo side to ensure that this type
of changes get detected early on. Additional work is also needed to
reduce the footprint of the (large) memory-tagging related structures
that are currently part of the allocator.
Differential Revision: https://reviews.llvm.org/D110575
Adds magic version header to AllocatorState. This can be used by
out-of-process crash handlers, like Crashpad on Fuchsia, to do offline
reconstruction of GWP-ASan crash metadata.
Crashpad on Fuchsia is intending on dumping the AllocationMetadata pool
and the AllocatorState directly into the minidump. Then, using the
version number, they can unpack the data on serverside using a versioned
unpack tool.
Also add some asserts to make sure the version number gets bumped if the
internal structs get changed.
Reviewed By: eugenis, mcgrathr
Differential Revision: https://reviews.llvm.org/D106690
This patch does a few cleanup things:
1. The non-standalone scudo has a problem where GWP-ASan allocations
may not meet alignment requirements where Scudo was requested to have
alignment >= 16. Use the new GWP-ASan API to fix this.
2. The standalone variant loses some debugging information inside of
GWP-ASan because we ask GWP-ASan to allocate an aligned size in the
frontend. This means reports end up with 'UaF on a 16-byte allocation'
for a 1-byte allocation with 16-byte alignment. Also use the new API to
fix this.
3. Add post-alloc hooks for GWP-ASan intercepted allocations, and add
stats tracking for GWP-ASan allocations.
4. Add a small test that checks the alignment of the frontend
allocator, so that it can be used under GWP-ASan torture mode.
5. Add GWP-ASan torture mode as a testing configuration to catch these
regressions.
Depends on D94830, D95889.
Reviewed By: cryptoad
Differential Revision: https://reviews.llvm.org/D95884
Adds a new allocation API to GWP-ASan that handles size+alignment
restrictions.
Reviewed By: cryptoad, eugenis
Differential Revision: https://reviews.llvm.org/D94830
Summary:
Forewarning: This patch looks big in #LOC changed. I promise it's not that bad, it just moves a lot of content from one file to another. I've gone ahead and left inline comments on Phabricator for sections where this has happened.
This patch:
1. Introduces the crash handler API (crash_handler_api.h).
2. Moves information required for out-of-process crash handling into an AllocatorState. This is a trivially-copied POD struct that designed to be recovered from a deceased process, and used by the crash handler to create a GWP-ASan report (along with the other trivially-copied Metadata struct).
3. Implements the crash handler API using the AllocatorState and Metadata.
4. Adds tests for the crash handler.
5. Reimplements the (now optionally linked by the supporting allocator) in-process crash handler (i.e. the segv handler) using the new crash handler API.
6. Minor updates Scudo & Scudo Standalone to fix compatibility.
7. Changed capitalisation of errors (e.g. /s/Use after free/Use After Free).
Reviewers: cryptoad, eugenis, jfb
Reviewed By: eugenis
Subscribers: merge_guards_bot, pcc, jfb, dexonsmith, mgorny, cryptoad, #sanitizers, llvm-commits
Tags: #sanitizers, #llvm
Differential Revision: https://reviews.llvm.org/D73557
