[PATCH v2 08/11] x86/boot: place trampoline code in a non-execute section

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

The trampoline code is never executed in the position placed by the
loader.  It's first copied to the low 1MB, and always executed from
there.

Move the trampoline code from being in .init.text section into
.init.data, so it's not in an executable section.  This allows applying
the relocations safely against a non-executable (and thus non-read only)
section, and then copy the relocated trampoline to the low 1MB.  Note
that the trampoline code is placed on an .init section, so zapped after
boot has finished.

No functional change intended.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
An alternative approach is to apply the relocations after having copied the
trampoline to the low 1MB, but that still generates relocations in mkreloc,
which is not helpful for the goal of having no relocations applied to
read-execute code sections.  This approach however places code in a data
section, which might cause issues when debugging it.
---
 xen/arch/x86/boot/head.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 774894954e44..f5a2d08d0d0e 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -709,7 +709,7 @@ trampoline_setup:
         /* Jump into the relocated trampoline. */
         lret
 
-        .section .init.text, "ax", @progbits
+        .section .init.data, "aw", @progbits
 ENTRY(trampoline_start)
 #include "trampoline.S"
 ENTRY(trampoline_end)
-- 
2.48.1