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From: Jan Beulich <jbeulich@suse.com>
Subject: x86/shadow: fix ref-counting error handling
The old-Linux handling in shadow_set_l4e() mistakenly ORed together the
results of sh_get_ref() and sh_pin(). As the latter failing is not a
correctness problem, simply ignore its return value.
In sh_set_toplevel_shadow() a failing sh_get_ref() must not be
accompanied by installing the entry, despite the domain being crashed.
This is XSA-250.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -923,7 +923,7 @@ static int shadow_set_l4e(struct domain
shadow_l4e_t new_sl4e,
mfn_t sl4mfn)
{
- int flags = 0, ok;
+ int flags = 0;
shadow_l4e_t old_sl4e;
paddr_t paddr;
ASSERT(sl4e != NULL);
@@ -938,15 +938,16 @@ static int shadow_set_l4e(struct domain
{
/* About to install a new reference */
mfn_t sl3mfn = shadow_l4e_get_mfn(new_sl4e);
- ok = sh_get_ref(d, sl3mfn, paddr);
- /* Are we pinning l3 shadows to handle wierd linux behaviour? */
- if ( sh_type_is_pinnable(d, SH_type_l3_64_shadow) )
- ok |= sh_pin(d, sl3mfn);
- if ( !ok )
+
+ if ( !sh_get_ref(d, sl3mfn, paddr) )
{
domain_crash(d);
return SHADOW_SET_ERROR;
}
+
+ /* Are we pinning l3 shadows to handle weird Linux behaviour? */
+ if ( sh_type_is_pinnable(d, SH_type_l3_64_shadow) )
+ sh_pin(d, sl3mfn);
}
/* Write the new entry */
@@ -3965,14 +3966,15 @@ sh_set_toplevel_shadow(struct vcpu *v,
/* Take a ref to this page: it will be released in sh_detach_old_tables()
* or the next call to set_toplevel_shadow() */
- if ( !sh_get_ref(d, smfn, 0) )
+ if ( sh_get_ref(d, smfn, 0) )
+ new_entry = pagetable_from_mfn(smfn);
+ else
{
SHADOW_ERROR("can't install %#lx as toplevel shadow\n", mfn_x(smfn));
domain_crash(d);
+ new_entry = pagetable_null();
}
- new_entry = pagetable_from_mfn(smfn);
-
install_new_entry:
/* Done. Install it */
SHADOW_PRINTK("%u/%u [%u] gmfn %#"PRI_mfn" smfn %#"PRI_mfn"\n",
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