File 5dbaf89f-dont-use-BUG-for-parameter-checking.patch of Package xen.17121

Overview Repositories Revisions Requests Users Attributes Meta

File 5dbaf89f-dont-use-BUG-for-parameter-checking.patch of Package xen.17121

# Commit 0bf9f8d3e399a0e1d2b717f71b4776172446184b
# Date 2019-10-31 16:07:11 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Jan Beulich <jbeulich@suse.com>
xen/hypercall: Don't use BUG() for parameter checking in hypercall_create_continuation()

Since c/s 1d429034 "hypercall: update vcpu_op to take an unsigned vcpuid",
which incorrectly swapped 'i' for 'u' in the parameter type list, guests have
been able to hit the BUG() in next_args()'s default case.

Correct these back to 'i'.

In addition, make adjustments to prevent this class of issue from occurring in
the future - crashing Xen is not an appropriate form of parameter checking.

Capitalise NEXT_ARG() to catch all uses, to highlight that it is a macro doing
non-function-like things behind the scenes, and undef it when appropriate.
Implement a bad_fmt: block which prints an error, asserts unreachable, and
crashes the guest.

On the ARM side, drop all parameter checking of p.  It is asymmetric with the
x86 side, and akin to expecting memcpy() or sprintf() to check their src/fmt
parameter before use.  A caller passing "" or something other than a string
literal will be obvious during code review.

This is XSA-296.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Julien Grall <julien.grall@arm.com>

# Commit df7a19338a892b5cf585fd2bee8584cb15e0cace
# Date 2019-11-21 15:50:01 +0000
# Author Julien Grall <julien@xen.org>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
xen: Add missing va_end() in hypercall_create_continuation()

The documentation requires va_start() to always be matched with a
corresponding va_end(). However, this is not the case in the path used
for bad format.

This was introduced by XSA-296.

Coverity-ID: 1488727
Fixes: 0bf9f8d3e3 ("xen/hypercall: Don't use BUG() for parameter checking in hypercall_create_continuation()")
Signed-off-by: Julien Grall <julien@xen.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -374,14 +374,15 @@ void sync_vcpu_execstate(struct vcpu *v)
     /* Nothing to do -- no lazy switching */
 }
 
-#define next_arg(fmt, args) ({                                              \
+#define NEXT_ARG(fmt, args)                                                 \
+({                                                                          \
     unsigned long __arg;                                                    \
     switch ( *(fmt)++ )                                                     \
     {                                                                       \
     case 'i': __arg = (unsigned long)va_arg(args, unsigned int);  break;    \
     case 'l': __arg = (unsigned long)va_arg(args, unsigned long); break;    \
     case 'h': __arg = (unsigned long)va_arg(args, void *);        break;    \
-    default:  __arg = 0; BUG();                                             \
+    default:  goto bad_fmt;                                                 \
     }                                                                       \
     __arg;                                                                  \
 })
@@ -396,9 +397,6 @@ unsigned long hypercall_create_continuat
     unsigned int i;
     va_list args;
 
-    /* All hypercalls take at least one argument */
-    BUG_ON( !p || *p == '\0' );
-
     current->hcall_preempted = true;
 
     va_start(args, format);
@@ -406,7 +404,7 @@ unsigned long hypercall_create_continuat
     if ( mcs->flags & MCSF_in_multicall )
     {
         for ( i = 0; *p != '\0'; i++ )
-            mcs->call.args[i] = next_arg(p, args);
+            mcs->call.args[i] = NEXT_ARG(p, args);
 
         /* Return value gets written back to mcs->call.result */
         rc = mcs->call.result;
@@ -422,7 +420,7 @@ unsigned long hypercall_create_continuat
 
             for ( i = 0; *p != '\0'; i++ )
             {
-                arg = next_arg(p, args);
+                arg = NEXT_ARG(p, args);
 
                 switch ( i )
                 {
@@ -445,7 +443,7 @@ unsigned long hypercall_create_continuat
 
             for ( i = 0; *p != '\0'; i++ )
             {
-                arg = next_arg(p, args);
+                arg = NEXT_ARG(p, args);
 
                 switch ( i )
                 {
@@ -466,8 +464,17 @@ unsigned long hypercall_create_continuat
     va_end(args);
 
     return rc;
+
+ bad_fmt:
+    va_end(args);
+    gprintk(XENLOG_ERR, "Bad hypercall continuation format '%c'\n", *p);
+    ASSERT_UNREACHABLE();
+    domain_crash(current->domain);
+    return 0;
 }
 
+#undef NEXT_ARG
+
 void startup_cpu_idle_loop(void)
 {
     struct vcpu *v = current;
--- a/xen/arch/x86/hypercall.c
+++ b/xen/arch/x86/hypercall.c
@@ -74,14 +74,15 @@ const hypercall_args_t hypercall_args_ta
 #undef COMP
 #undef ARGS
 
-#define next_arg(fmt, args) ({                                              \
+#define NEXT_ARG(fmt, args)                                                 \
+({                                                                          \
     unsigned long __arg;                                                    \
     switch ( *(fmt)++ )                                                     \
     {                                                                       \
     case 'i': __arg = (unsigned long)va_arg(args, unsigned int);  break;    \
     case 'l': __arg = (unsigned long)va_arg(args, unsigned long); break;    \
     case 'h': __arg = (unsigned long)va_arg(args, void *);        break;    \
-    default:  __arg = 0; BUG();                                             \
+    default:  goto bad_fmt;                                                 \
     }                                                                       \
     __arg;                                                                  \
 })
@@ -103,7 +104,7 @@ unsigned long hypercall_create_continuat
     if ( mcs->flags & MCSF_in_multicall )
     {
         for ( i = 0; *p != '\0'; i++ )
-            mcs->call.args[i] = next_arg(p, args);
+            mcs->call.args[i] = NEXT_ARG(p, args);
     }
     else
     {
@@ -115,7 +116,7 @@ unsigned long hypercall_create_continuat
         {
             for ( i = 0; *p != '\0'; i++ )
             {
-                arg = next_arg(p, args);
+                arg = NEXT_ARG(p, args);
                 switch ( i )
                 {
                 case 0: regs->rdi = arg; break;
@@ -131,7 +132,7 @@ unsigned long hypercall_create_continuat
         {
             for ( i = 0; *p != '\0'; i++ )
             {
-                arg = next_arg(p, args);
+                arg = NEXT_ARG(p, args);
                 switch ( i )
                 {
                 case 0: regs->rbx = arg; break;
@@ -148,8 +149,17 @@ unsigned long hypercall_create_continuat
     va_end(args);
 
     return op;
+
+ bad_fmt:
+    va_end(args);
+    gprintk(XENLOG_ERR, "Bad hypercall continuation format '%c'\n", *p);
+    ASSERT_UNREACHABLE();
+    domain_crash(curr->domain);
+    return 0;
 }
 
+#undef NEXT_ARG
+
 int hypercall_xlat_continuation(unsigned int *id, unsigned int nr,
                                 unsigned int mask, ...)
 {
--- a/xen/common/compat/domain.c
+++ b/xen/common/compat/domain.c
@@ -81,7 +81,7 @@ int compat_vcpu_op(int cmd, unsigned int
         }
 
         if ( rc == -ERESTART )
-            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iuh",
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
                                                cmd, vcpuid, arg);
 
         break;
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1298,7 +1298,7 @@ long do_vcpu_op(int cmd, unsigned int vc
 
         rc = arch_initialise_vcpu(v, arg);
         if ( rc == -ERESTART )
-            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iuh",
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
                                                cmd, vcpuid, arg);
 
         break;

Places

File 5dbaf89f-dont-use-BUG-for-parameter-checking.patch of Package xen.17121

Places