Re: is_loadable_phdr

[Brad Plant <bplant@iinet.net.au>]

[-- Attachment #1.1.1: Type: text/plain, Size: 1023 bytes --]

On Thu, 28 Jan 2010 21:14:14 +0000
Keir Fraser <keir.fraser@eu.citrix.com> wrote:

> On 28/01/2010 19:55, "Brad Plant" <bplant@iinet.net.au> wrote:
> 
> > I'm trying to get an understanding of why a segment has to be writeable or
> > executable for xen to load it. Does anyone know why this is so?
> > 
> > Also, is it likely that this behaviour could be changed? My understanding is
> > that it's perfectly valid to have an ELF kernel with read-only segments in it.
> > Attempting to use an image with a read-only segment leads to the kernel
> > failing to boot with weird and hard to debug crashes.
> 
> Yes, we can change that. Send a patch for it.

So there's no reason not loading read-only segments then?

I've attached a patch that'll change elf_phdr_is_loadable's behaviour. It just adds PF_R into the mix. I don't know if this will cause some unwanted side effects. Unfortunately there'll be some very unhappy people if I go rebooting an entire physical machine at the moment.

Cheers,

Brad

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1.1.2: libelf-tools.c.patch --]
[-- Type: text/x-patch, Size: 485 bytes --]

--- xen/common/libelf/libelf-tools.c.orig	2010-01-29 08:44:48.000000000 +1100
+++ xen/common/libelf/libelf-tools.c	2010-01-29 08:59:18.000000000 +1100
@@ -235,7 +235,7 @@ int elf_phdr_is_loadable(struct elf_bina
     uint64_t p_type = elf_uval(elf, phdr, p_type);
     uint64_t p_flags = elf_uval(elf, phdr, p_flags);
 
-    return ((p_type == PT_LOAD) && (p_flags & (PF_W | PF_X)) != 0);
+    return ((p_type == PT_LOAD) && (p_flags & (PF_R | PF_W | PF_X)) != 0);
 }
 
 /*

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 197 bytes --]

[-- Attachment #2: Type: text/plain, Size: 138 bytes --]

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel