Re: [Qemu-devel] [PATCH] fix interaction with noexecstack

[Fabrice Bellard <fabrice@bellard.org>]

The patch seems OK for me, at least until the instruction cache is 
dynamically allocated.

Fabrice.

Lennert Buytenhek wrote:
> Hi,
> 
> qemu-arm doesn't work on Fedora Core 2 by default because it expects to
> be able to execute stuff off the heap (code_gen_buffer), but that part of
> the heap is not marked PROT_EXEC, and Fedora Core 2 has a patch that sets
> the CS segment limit to the highest PROT_EXEC-mapped address in the address
> space.
> 
> It's a bit of a hacky fix, but it Works For Me(tm) on the default Fedora
> 2.6.5 kernel.  I haven't yet looked into why qemu-arm was crashing on the
> Fedora 2.6.[78] update kernels.
> 
> 
> --L
> 
> 
> diff -urN qemu-20040804.orig/exec.c qemu-20040804.test/exec.c
> --- qemu-20040804.orig/exec.c	2004-07-06 02:00:18.000000000 +0300
> +++ qemu-20040804.test/exec.c	2004-09-04 02:49:25.414945456 +0300
> @@ -127,6 +127,9 @@
>  
>  static void page_init(void)
>  {
> +    unsigned long address;
> +    unsigned long length;
> +
>      /* NOTE: we can always suppose that qemu_host_page_size >=
>         TARGET_PAGE_SIZE */
>  #ifdef _WIN32
> @@ -134,6 +137,17 @@
>  #else
>      qemu_real_host_page_size = getpagesize();
>  #endif
> +
> +    address = (unsigned long)code_gen_buffer;
> +    address &= ~(qemu_real_host_page_size - 1);
> +
> +    length = (unsigned long)code_gen_buffer + sizeof(code_gen_buffer);
> +    length -= address;
> +    length += qemu_real_host_page_size - 1;
> +    length &= ~(qemu_real_host_page_size - 1);
> +
> +    mprotect(address, length, PROT_READ | PROT_WRITE | PROT_EXEC);
> +
>      if (qemu_host_page_size == 0)
>          qemu_host_page_size = qemu_real_host_page_size;
>      if (qemu_host_page_size < TARGET_PAGE_SIZE)
> 
> 
> 
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