kexec: Avoid unaligned writes when producing crash info.

The alignment of info is 32bits in line with the elf specification.
This means that on 64 bit architectures accessing it directly may
result unaligned access and a panic. I have been experiencing
this on IA64.

It seems that a simple approach of having an crash_xen_info_t on
the stack and simply memcopying it into info at the end alleviates
the problem.

Signed-off-by: Simon Horman <horms@verge.net.au>

diff --git a/xen/common/kexec.c b/xen/common/kexec.c
index 80314a6673b162e8aaaca2829e522db156dd0210..c0fe6d239622d324ffb5f5af970c0fb6807f7e14 100644 (file)
--- a/xen/common/kexec.c
+++ b/xen/common/kexec.c
@@ -81,20 +81,25 @@ void kexec_crash_save_cpu(void)
 crash_xen_info_t *kexec_crash_save_info(void)
 {
     int cpu = smp_processor_id();
-    crash_xen_info_t *info = (crash_xen_info_t *)ELFNOTE_DESC(xen_crash_note);
+    crash_xen_info_t info;
+    crash_xen_info_t *out = (crash_xen_info_t *)ELFNOTE_DESC(xen_crash_note);
 
     BUG_ON(!cpu_test_and_set(cpu, crash_saved_cpus));
 
-    info->xen_major_version = xen_major_version();
-    info->xen_minor_version = xen_minor_version();
-    info->xen_extra_version = __pa(xen_extra_version());
-    info->xen_changeset = __pa(xen_changeset());
-    info->xen_compiler = __pa(xen_compiler());
-    info->xen_compile_date = __pa(xen_compile_date());
-    info->xen_compile_time = __pa(xen_compile_time());
-    info->tainted = tainted;
+    memset(&info, 0, sizeof(info));
+    info.xen_major_version = xen_major_version();
+    info.xen_minor_version = xen_minor_version();
+    info.xen_extra_version = __pa(xen_extra_version());
+    info.xen_changeset = __pa(xen_changeset());
+    info.xen_compiler = __pa(xen_compiler());
+    info.xen_compile_date = __pa(xen_compile_date());
+    info.xen_compile_time = __pa(xen_compile_time());
+    info.tainted = tainted;
 
-    return info;
+    /* Copy from guaranteed-aligned local copy to possibly-unaligned dest. */
+    memcpy(out, &info, sizeof(info));
+
+    return out;
 }
 
 void kexec_crash(void)