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Adobe Flash incorrect jit optimization with op_pushwith #112

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
The avmplus bytecode verifier misses a control-flow path via op_pushwith 
throwing an exception allowing crafted bytecode to be incorrectly optimized 
which can trivially be abused to get code execution.

The avm2 spec [ 
http://www.adobe.com/content/dam/Adobe/en/devnet/actionscript/articles/avm2overv
iew.pdf ] actually notes that pushwith can throw an exception: 

(p.97:)
...
Runtime exceptions 
A TypeError is thrown if scope_obj is null or undefined
...

This isn't reflected in opcodes.tbl however meaning that the verifier won't add 
a control flow edge between a pushwith and any catch blocks associated with 
enclosing try blocks:

  //              opCount  throw  stack  internal  name                   hex 
  ABC_OP(         0,       0,     -1,    0,        pushwith)              // 0x1C  

Looking at the implementation of the verifier and codegen for pushwith:

Verifier.cpp:
...
            case OP_pushwith:
            {
                checkStack(1,0);

                if (state->scopeDepth + 1 > ms->max_scope())
                    verifyFailed(kScopeStackOverflowError);

                emitCheckNull(sp);                <-- this can throw
                coder->writeOp1(state, pc, opcode, ms->scope_base() + state->scopeDepth);

                Traits* scopeTraits = state->peek().traits;
                state->pop();
                state->setType(ms->scope_base() + state->scopeDepth, scopeTraits, true, true);

                if (state->withBase == -1)
                    state->withBase = state->scopeDepth;

                state->scopeDepth++;
                break;
...

the emitCheckNull will emit code which throws a catchable exception if the 
scope object passed on the stack is NULL. This is exactly what the attached PoC 
does; it uses the same technique as the previous PoC to use this to confuse the 
jit engine into emitting incorrectly optimized code.

Tested against the latest version of flash projector (15.0.0.152) on OS X

Original issue reported on code.google.com by ianb...@google.com on 21 Sep 2014 at 4:42

Attachments:

GoogleCodeExporter commented 9 years ago

Original comment by ianb...@google.com on 22 Sep 2014 at 11:59

GoogleCodeExporter commented 9 years ago

Original comment by ianb...@google.com on 23 Sep 2014 at 7:14

GoogleCodeExporter commented 9 years ago

Original comment by cev...@google.com on 8 Nov 2014 at 2:35

GoogleCodeExporter commented 9 years ago 
http://helpx.adobe.com/security/products/flash-player/apsb14-24.html

Original comment by cev...@google.com on 20 Nov 2014 at 1:23