A little more information on this from here [5]:
You also have the option of dynamically controlling the set of icall
target addresses that are considered valid by CFG using the
SetProcessValidCallTargets [1] from the Memory Management API. The same
API can be used to specify whether pages are invalid or valid targets
for CFG. The VirtualProtect [2] and VirtualAlloc [3] functions will by
default treat a specified region of executable and committed pages as
valid indirect call targets. It is possible to override this behavior,
such as when implementing a Just-in-Time compiler, by specifying
PAGE_TARGETS_INVALID when calling VirtualAlloc or
PAGE_TARGETS_NO_UPDATE when calling VirtualProtect as detailed under
Memory Protection Constants [4].
On 2024-01-17 19:25, Brad Robinson via Tinycc-devel wrote:
Hi All,
I'm trying to use setjmp/longjmp in code that needs to be compiled to
in-memory.
On Windows 11 (and presumably Windows 10) when you have Control Flow
Guard enabled, it crashes on calling longjmp.
If compiled to .exe it works fine. When Control Flow Guard is disabled
(Control Panel ... -> ... Exploit Protection) is works fine.
I've read up a little on this and it seems like it's an exception being
thrown in kernel, by a call to check the call target from the CRT.
I've also read that the call target should be allowed if the target
address' page has been marked executable - so I think this should work,
but it's definitely not.
Sample program test.c below that fails in the longjmp call when running
`tcc -run test.c`
Any ideas?
Brad
#include <stdio.h>
#include <setjmp.h>
jmp_buf jmpbuf;
void my_function()
{
longjmp(jmpbuf, 1);
}
int main()
{
if (setjmp(jmpbuf) == 0)
{
printf("A\n");
my_function();
printf("B\n");
}
printf("C\n");
return 0;
}
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Links:
------
[1]
https://learn.microsoft.com/en-us/windows/desktop/api/memoryapi/nf-memoryapi-setprocessvalidcalltargets
[2]
https://learn.microsoft.com/en-us/windows/desktop/api/memoryapi/nf-memoryapi-virtualprotect
[3]
https://learn.microsoft.com/en-us/windows/desktop/api/memoryapi/nf-memoryapi-virtualalloc
[4]
https://learn.microsoft.com/en-us/windows/desktop/Memory/memory-protection-constants
[5]
https://learn.microsoft.com/en-us/windows/win32/secbp/control-flow-guard_______________________________________________
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