Mailing List Archive

commit 7b032c259128b61cc73d1f764bbd88254fd5a315
Author: Andrew Cooper <andrew.cooper3@citrix.com>
AuthorDate: Mon Nov 4 15:01:56 2019 +0100
Commit: Jan Beulich <jbeulich@suse.com>
CommitDate: Mon Nov 4 15:01:56 2019 +0100

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>
master commit: 0bf9f8d3e399a0e1d2b717f71b4776172446184b
master date: 2019-10-31 16:07:11 +0100
---
xen/arch/arm/domain.c | 22 ++++++++++++++--------
xen/arch/x86/hypercall.c | 19 ++++++++++++++-----
xen/common/compat/domain.c | 2 +-
xen/common/domain.c | 2 +-
4 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 2ab315ea6f..0b6d477d7f 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -347,14 +347,15 @@ 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; \
})
@@ -374,9 +375,6 @@ unsigned long hypercall_create_continuation(
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);
@@ -384,7 +382,7 @@ unsigned long hypercall_create_continuation(
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;
@@ -400,7 +398,7 @@ unsigned long hypercall_create_continuation(

for ( i = 0; *p != '\0'; i++ )
{
- arg = next_arg(p, args);
+ arg = NEXT_ARG(p, args);

switch ( i )
{
@@ -423,7 +421,7 @@ unsigned long hypercall_create_continuation(

for ( i = 0; *p != '\0'; i++ )
{
- arg = next_arg(p, args);
+ arg = NEXT_ARG(p, args);

switch ( i )
{
@@ -444,8 +442,16 @@ unsigned long hypercall_create_continuation(
va_end(args);

return rc;
+
+ bad_fmt:
+ 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;
diff --git a/xen/arch/x86/hypercall.c b/xen/arch/x86/hypercall.c
index e30181817a..ae2f1ba187 100644
--- a/xen/arch/x86/hypercall.c
+++ b/xen/arch/x86/hypercall.c
@@ -74,14 +74,15 @@ const hypercall_args_t hypercall_args_table[NR_hypercalls] =
#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; \
})
@@ -108,7 +109,7 @@ unsigned long hypercall_create_continuation(
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
{
@@ -120,7 +121,7 @@ unsigned long hypercall_create_continuation(
{
for ( i = 0; *p != '\0'; i++ )
{
- arg = next_arg(p, args);
+ arg = NEXT_ARG(p, args);
switch ( i )
{
case 0: regs->rdi = arg; break;
@@ -136,7 +137,7 @@ unsigned long hypercall_create_continuation(
{
for ( i = 0; *p != '\0'; i++ )
{
- arg = next_arg(p, args);
+ arg = NEXT_ARG(p, args);
switch ( i )
{
case 0: regs->rbx = arg; break;
@@ -153,8 +154,16 @@ unsigned long hypercall_create_continuation(
va_end(args);

return op;
+
+ bad_fmt:
+ 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, ...)
{
diff --git a/xen/common/compat/domain.c b/xen/common/compat/domain.c
index 88bfdc836d..d446ed131b 100644
--- a/xen/common/compat/domain.c
+++ b/xen/common/compat/domain.c
@@ -81,7 +81,7 @@ int compat_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) ar
}

if ( rc == -ERESTART )
- rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iuh",
+ rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
cmd, vcpuid, arg);

break;
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 1bfec32e9c..a49545121b 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1273,7 +1273,7 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)

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;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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