[PATCH][HVM] HVM guest creation crashing with 1 MB of guest memory

[PATCH][HVM] HVM guest creation crashing with 1 MB of guest memory

[Andre Przywara]

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Hi,

When an HVM guest is started and assigned exactly one Megabyte of RAM, 
XEN will crash due to a overflow in building the E820 map in line 90 of 
tools/libxc/xc_hvm_build.c:
e820entry[nr_map].size = mem_size - 0x100000 - PAGE_SIZE * 3;
If memsize is one MB, the result will be negative (and the member is 
unsigned). As I don't think this is worth fixing here, I simply 
increased the minimal required memory for guest from zero to one 
Megabyte. Could someone check the effect on paravirtualized guests?

Regards,
Andre.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>

--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany

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vertretungsberechtigter Komplementär: AMD Saxony LLC (Sitz Wilmington, 
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Geschäftsführer der AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy

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diff -r 3a5722420de7 tools/python/xen/xend/XendConfig.py
--- a/tools/python/xen/xend/XendConfig.py	Thu May 03 19:25:47 2007 +0100
+++ b/tools/python/xen/xend/XendConfig.py	Fri May 04 15:41:15 2007 +0200
@@ -360,9 +360,9 @@ class XendConfig(dict):
         if not self["memory_dynamic_max"] <= self["memory_static_max"]:
             raise XendConfigError("memory_dynamic_max must be less " \
                                   "than or equal to memory_static_max")
-        if not self["memory_dynamic_max"] > 0:
+        if not self["memory_dynamic_max"] > 1048576:
             raise XendConfigError("memory_dynamic_max must be greater " \
-                                  "than zero")
+                                  "than one MB")
         if not self["memory_static_max"] > 0:
             raise XendConfigError("memory_static_max must be greater " \
                                   "than zero")

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Re: [PATCH][HVM] HVM guest creation crashing with 1 MB of guest memory

[Keir Fraser]

On 4/5/07 14:47, "Andre Przywara" <andre.przywara@amd.com> wrote:

> When an HVM guest is started and assigned exactly one Megabyte of RAM,
> XEN will crash due to a overflow in building the E820 map in line 90 of
> tools/libxc/xc_hvm_build.c:
> e820entry[nr_map].size = mem_size - 0x100000 - PAGE_SIZE * 3;
> If memsize is one MB, the result will be negative (and the member is
> unsigned). As I don't think this is worth fixing here, I simply
> increased the minimal required memory for guest from zero to one
> Megabyte. Could someone check the effect on paravirtualized guests?

Better to check and reject the memory size in xc_hvm_build() itself. I'll
make a patch to do this.

 -- Keir