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Tests demonstrating pointer-encoding unsoundness #5823

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Merged
merged 1 commit into from
Feb 16, 2021
Merged

Tests demonstrating pointer-encoding unsoundness #5823

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11 changes: 11 additions & 0 deletions regression/cbmc/Pointer_Arithmetic18/main.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
#define MB 0x00100000
#define BASE (15 * MB)
#define OFFSET (1 * MB)

main()
{
char *base = BASE;
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I'm a little concerned by this. As I understand CBMC's memory model we do not support literal addresses. I don't think we are required to do so by the standard either.

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I'd say we half-support them... And I'd really like to see that fixed as well, might just happen along the way ;-)

int offset = OFFSET;
__CPROVER_assert(
&((char *)base)[offset] >= BASE + OFFSET, "no wrap-around expected");
}
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This one feels like it's a bit overfitted to the current encoding -- how about checking that the conversion to an integer doesn't get smaller?

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Done.

8 changes: 8 additions & 0 deletions regression/cbmc/Pointer_Arithmetic18/test.desc
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KNOWNBUG
main.c
--32
^EXIT=0$
^SIGNAL=0$
^VERIFICATION SUCCESSFUL$
--
^warning: ignoring
22 changes: 22 additions & 0 deletions regression/cbmc/Pointer_comparison1/main.c
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#include <stdlib.h>

int main()
{
if(sizeof(void *) != 8)
return 0;

char *p = malloc(1);
if(p == 0)
return 0;

if(
(unsigned long)p >
42) // unsoundly evaluates to true due to pointer encoding
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Is this unsound? ISO-9899 allows conversion of pointers to integers but doesn't say what they will be. Thinking about actual platforms, this kind of thing could be ASLR dependent!

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Agreed, and I would thus argue that the assertion below ought to be considered reachable by a sound verification tool (i.e., there exists some system configuration under which p is less or equal to 42).

{
return 0;
}

__CPROVER_assert(0, "");

return 0;
}
8 changes: 8 additions & 0 deletions regression/cbmc/Pointer_comparison1/test.desc
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KNOWNBUG
main.c

^EXIT=10$
^SIGNAL=0$
^VERIFICATION FAILED$
--
^warning: ignoring