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x86: limit checks in hypercall_xlat_continuation() to actual arguments
HVM/PVH guests can otherwise trigger the final BUG_ON() in that
function by entering 64-bit mode, setting the high halves of affected
registers to non-zero values, leaving 64-bit mode, and issuing a
hypercall that might get preempted and hence become subject to
continuation argument translation (HYPERVISOR_memory_op being the only
one possible for HVM, PVH also having the option of using
HYPERVISOR_mmuext_op). This issue got introduced when HVM code was
switched to use compat_memory_op() - neither that nor
hypercall_xlat_continuation() were originally intended to be used by
other than PV guests (which can't enter 64-bit mode and hence have no
way to alter the high halves of 64-bit registers).
This is XSA-111.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1750,7 +1750,8 @@ unsigned long hypercall_create_continuat
return op;
}
-int hypercall_xlat_continuation(unsigned int *id, unsigned int mask, ...)
+int hypercall_xlat_continuation(unsigned int *id, unsigned int nr,
+ unsigned int mask, ...)
{
int rc = 0;
struct mc_state *mcs = ¤t->mc_state;
@@ -1759,7 +1760,10 @@ int hypercall_xlat_continuation(unsigned
unsigned long nval = 0;
va_list args;
- BUG_ON(id && *id > 5);
+ ASSERT(nr <= ARRAY_SIZE(mcs->call.args));
+ ASSERT(!(mask >> nr));
+
+ BUG_ON(id && *id >= nr);
BUG_ON(id && (mask & (1U << *id)));
va_start(args, mask);
@@ -1772,7 +1776,7 @@ int hypercall_xlat_continuation(unsigned
return 0;
}
- for ( i = 0; i < 6; ++i, mask >>= 1 )
+ for ( i = 0; i < nr; ++i, mask >>= 1 )
{
if ( mask & 1 )
{
@@ -1800,7 +1804,7 @@ int hypercall_xlat_continuation(unsigned
else
{
regs = guest_cpu_user_regs();
- for ( i = 0; i < 6; ++i, mask >>= 1 )
+ for ( i = 0; i < nr; ++i, mask >>= 1 )
{
unsigned long *reg;
--- a/xen/arch/x86/x86_64/compat/mm.c
+++ b/xen/arch/x86/x86_64/compat/mm.c
@@ -118,7 +118,7 @@ int compat_arch_memory_op(unsigned long
break;
if ( rc == __HYPERVISOR_memory_op )
- hypercall_xlat_continuation(NULL, 0x2, nat, arg);
+ hypercall_xlat_continuation(NULL, 2, 0x2, nat, arg);
XLAT_pod_target(&cmp, nat);
@@ -354,7 +354,7 @@ int compat_mmuext_op(XEN_GUEST_HANDLE_PA
left = 1;
if ( arg1 != MMU_UPDATE_PREEMPTED )
{
- BUG_ON(!hypercall_xlat_continuation(&left, 0x01, nat_ops,
+ BUG_ON(!hypercall_xlat_continuation(&left, 4, 0x01, nat_ops,
cmp_uops));
if ( !test_bit(_MCSF_in_multicall, &mcs->flags) )
regs->_ecx += count - i;
@@ -362,7 +362,7 @@ int compat_mmuext_op(XEN_GUEST_HANDLE_PA
mcs->compat_call.args[1] += count - i;
}
else
- BUG_ON(hypercall_xlat_continuation(&left, 0));
+ BUG_ON(hypercall_xlat_continuation(&left, 4, 0));
BUG_ON(left != arg1);
}
else
--- a/xen/common/compat/memory.c
+++ b/xen/common/compat/memory.c
@@ -282,7 +282,7 @@ int compat_memory_op(unsigned int cmd, X
break;
cmd = 0;
- if ( hypercall_xlat_continuation(&cmd, 0x02, nat.hnd, compat) )
+ if ( hypercall_xlat_continuation(&cmd, 2, 0x02, nat.hnd, compat) )
{
BUG_ON(rc != __HYPERVISOR_memory_op);
BUG_ON((cmd & MEMOP_CMD_MASK) != op);
--- a/xen/include/xen/compat.h
+++ b/xen/include/xen/compat.h
@@ -195,6 +195,8 @@ static inline int name(k xen_ ## n *x, k
* This option is useful for extracting the "op" argument or similar from the
* hypercall to enable further xlat processing.
*
+ * nr: Total number of arguments the hypercall has.
+ *
* mask: Specifies which of the hypercall arguments require compat translation.
* bit 0 indicates that the 0'th argument requires translation, bit 1 indicates
* that the first argument requires translation and so on. Native and compat
@@ -214,7 +216,8 @@ static inline int name(k xen_ ## n *x, k
*
* Return: Number of arguments which were actually translated.
*/
-int hypercall_xlat_continuation(unsigned int *id, unsigned int mask, ...);
+int hypercall_xlat_continuation(unsigned int *id, unsigned int nr,
+ unsigned int mask, ...);
/* In-place translation functons: */
struct start_info;
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