[Git][ghc/ghc][master] rts: fix pointer overflow undefined behavior in bytecode interpreter

[Marge Bot (@marge-bot)]

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
5bcfefd5 by Cheng Shao at 2024-10-17T23:04:09-04:00
rts: fix pointer overflow undefined behavior in bytecode interpreter

This patch fixes an unnoticed undefined behavior in the bytecode
interpreter. It can be caught by building `rts/Interpreter.c` with
`-fsanitize=pointer-overflow`, the warning message is something like:

```
rts/Interpreter.c:1369:13: runtime error: addition of unsigned offset to 0x004200197660 overflowed to 0x004200197658
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior rts/Interpreter.c:1369:13
rts/Interpreter.c:1265:13: runtime error: addition of unsigned offset to 0x004200197660 overflowed to 0x004200197658
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior rts/Interpreter.c:1265:13
rts/Interpreter.c:1645:13: runtime error: addition of unsigned offset to 0x0042000b22f8 overflowed to 0x0042000b22f0
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior rts/Interpreter.c:1645:13
```

Whenever we do something like `SpW(-1)`, the negative argument is
implicitly converted to an unsigned integer type and causes pointer
arithmetic overflow. It happens to be harmless for most targets since
overflowing would wrap the result to desired value, but it's still
coincidental and undefined behavior. Furthermore, it causes real
damage to the wasm backend, given clang-20 will emit invalid wasm code
that crashes at run-time for this kind of C code! (see
https://github.com/llvm/llvm-project/issues/108770)

The fix here is adding some explicit casts to ensure we always use the
signed `ptrdiff_t` type as right hand operand of pointer arithmetic.

- - - - -


1 changed file:

- rts/Interpreter.c


Changes:

=====================================
rts/Interpreter.c
=====================================
@@ -157,11 +157,11 @@ tag functions as tag inference currently doesn't rely on those being properly ta
    cap->r.rRet = (retcode);                             \
    return cap;
 
-#define Sp_plusB(n)  ((void *)(((StgWord8*)Sp) + (n)))
-#define Sp_minusB(n) ((void *)(((StgWord8*)Sp) - (n)))
+#define Sp_plusB(n)  ((void *)((StgWord8*)Sp + (ptrdiff_t)(n)))
+#define Sp_minusB(n) ((void *)((StgWord8*)Sp - (ptrdiff_t)(n)))
 
-#define Sp_plusW(n)  (Sp_plusB((n) * sizeof(W_)))
-#define Sp_minusW(n) (Sp_minusB((n) * sizeof(W_)))
+#define Sp_plusW(n)  (Sp_plusB((ptrdiff_t)(n) * (ptrdiff_t)sizeof(W_)))
+#define Sp_minusW(n) (Sp_minusB((ptrdiff_t)(n) * (ptrdiff_t)sizeof(W_)))
 
 #define Sp_addB(n)   (Sp = Sp_plusB(n))
 #define Sp_subB(n)   (Sp = Sp_minusB(n))



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5bcfefd5bb73c18a9bad63d1813968832b696f9a

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5bcfefd5bb73c18a9bad63d1813968832b696f9a
You're receiving this email because of your account on gitlab.haskell.org.


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-commits/attachments/20241017/1e3a68fe/attachment-0001.html>