[llvm] r351838 - [docs] Scudo: document error messages & their potential cause
Kostya Kortchinsky via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 22 08:43:45 PST 2019
Author: cryptoad
Date: Tue Jan 22 08:43:45 2019
New Revision: 351838
URL: http://llvm.org/viewvc/llvm-project?rev=351838&view=rev
Log:
[docs] Scudo: document error messages & their potential cause
Summary:
A couple of changes in the Scudo documentation:
- tag the shell code blocks as `console`;
- document error messages that are displayed in some termination conditions,
the reason they triggered, and potential causes.
Reviewers: eugenis, enh
Reviewed By: eugenis
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D56857
Modified:
llvm/trunk/docs/ScudoHardenedAllocator.rst
Modified: llvm/trunk/docs/ScudoHardenedAllocator.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/ScudoHardenedAllocator.rst?rev=351838&r1=351837&r2=351838&view=diff
==============================================================================
--- llvm/trunk/docs/ScudoHardenedAllocator.rst (original)
+++ llvm/trunk/docs/ScudoHardenedAllocator.rst Tue Jan 22 08:43:45 2019
@@ -108,7 +108,7 @@ functions.
You may also build Scudo like this:
-.. code::
+.. code:: console
cd $LLVM/projects/compiler-rt/lib
clang++ -fPIC -std=c++11 -msse4.2 -O2 -I. scudo/*.cpp \
@@ -117,7 +117,7 @@ You may also build Scudo like this:
and then use it with existing binaries as follows:
-.. code::
+.. code:: console
LD_PRELOAD=`pwd`/libscudo.so ./a.out
@@ -151,7 +151,7 @@ can be assigned in the same string, sepa
For example, using the environment variable:
-.. code::
+.. code:: console
SCUDO_OPTIONS="DeleteSizeMismatch=1:QuarantineSizeKb=64" ./a.out
@@ -201,3 +201,53 @@ Allocator related common Sanitizer optio
options, such as ``allocator_may_return_null`` or ``abort_on_error``. A detailed
list including those can be found here:
https://github.com/google/sanitizers/wiki/SanitizerCommonFlags.
+
+Error Types
+===========
+
+The allocator will output an error message, and potentially terminate the
+process, when an unexpected behavior is detected. The output usually starts with
+``"Scudo ERROR:"`` followed by a short summary of the problem that occurred as
+well as the pointer(s) involved. Once again, Scudo is meant to be a mitigation,
+and might not be the most useful of tools to help you root-cause the issue,
+please consider `ASan <https://github.com/google/sanitizers/wiki/AddressSanitizer>`_
+for this purpose.
+
+Here is a list of the current error messages and their potential cause:
+
+- ``"corrupted chunk header"``: the checksum verification of the chunk header
+ has failed. This is likely due to one of two things: the header was
+ overwritten (partially or totally), or the pointer passed to the function is
+ not a chunk at all;
+
+- ``"race on chunk header"``: two different threads are attempting to manipulate
+ the same header at the same time. This is usually symptomatic of a
+ race-condition or general lack of locking when performing operations on that
+ chunk;
+
+- ``"invalid chunk state"``: the chunk is not in the expected state for a given
+ operation, eg: it is not allocated when trying to free it, or it's not
+ quarantined when trying to recycle it, etc. A double-free is the typical
+ reason this error would occur;
+
+- ``"misaligned pointer"``: we strongly enforce basic alignment requirements, 8
+ bytes on 32-bit platforms, 16 bytes on 64-bit platforms. If a pointer passed
+ to our functions does not fit those, something is definitely wrong.
+
+- ``"allocation type mismatch"``: when the optional deallocation type mismatch
+ check is enabled, a deallocation function called on a chunk has to match the
+ type of function that was called to allocate it. Security implications of such
+ a mismatch are not necessarily obvious but situational at best;
+
+- ``"invalid sized delete"``: when the C++14 sized delete operator is used, and
+ the optional check enabled, this indicates that the size passed when
+ deallocating a chunk is not congruent with the one requested when allocating
+ it. This is likely to be a `compiler issue <https://software.intel.com/en-us/forums/intel-c-compiler/topic/783942>`_,
+ as was the case with Intel C++ Compiler, or some type confusion on the object
+ being deallocated;
+
+- ``"RSS limit exhausted"``: the maximum RSS optionally specified has been
+ exceeded;
+
+Several other error messages relate to parameter checking on the libc allocation
+APIs and are fairly straightforward to understand.
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