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x86: properly handle hvm_copy_from_guest_{phys,virt}() errors
Ignoring them generally implies using uninitialized data and, in all
cases dealt with here, potentially leaking hypervisor stack contents to
guests.
This is XSA-63.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2308,11 +2308,7 @@ void hvm_task_switch(
rc = hvm_copy_from_guest_virt(
&tss, prev_tr.base, sizeof(tss), PFEC_page_present);
- if ( rc == HVMCOPY_bad_gva_to_gfn )
- goto out;
- if ( rc == HVMCOPY_gfn_paged_out )
- goto out;
- if ( rc == HVMCOPY_gfn_shared )
+ if ( rc != HVMCOPY_okay )
goto out;
eflags = regs->eflags;
@@ -2357,13 +2353,11 @@ void hvm_task_switch(
rc = hvm_copy_from_guest_virt(
&tss, tr.base, sizeof(tss), PFEC_page_present);
- if ( rc == HVMCOPY_bad_gva_to_gfn )
- goto out;
- if ( rc == HVMCOPY_gfn_paged_out )
- goto out;
- /* Note: this could be optimised, if the callee functions knew we want RO
- * access */
- if ( rc == HVMCOPY_gfn_shared )
+ /*
+ * Note: The HVMCOPY_gfn_shared case could be optimised, if the callee
+ * functions knew we want RO access.
+ */
+ if ( rc != HVMCOPY_okay )
goto out;
--- a/xen/arch/x86/hvm/intercept.c
+++ b/xen/arch/x86/hvm/intercept.c
@@ -87,17 +87,28 @@ static int hvm_mmio_access(struct vcpu *
{
for ( i = 0; i < p->count; i++ )
{
- int ret;
-
- ret = hvm_copy_from_guest_phys(&data,
- p->data + (sign * i * p->size),
- p->size);
- if ( (ret == HVMCOPY_gfn_paged_out) ||
- (ret == HVMCOPY_gfn_shared) )
+ switch ( hvm_copy_from_guest_phys(&data,
+ p->data + sign * i * p->size,
+ p->size) )
{
+ case HVMCOPY_okay:
+ break;
+ case HVMCOPY_gfn_paged_out:
+ case HVMCOPY_gfn_shared:
rc = X86EMUL_RETRY;
break;
+ case HVMCOPY_bad_gfn_to_mfn:
+ data = ~0;
+ break;
+ case HVMCOPY_bad_gva_to_gfn:
+ ASSERT(0);
+ /* fall through */
+ default:
+ rc = X86EMUL_UNHANDLEABLE;
+ break;
}
+ if ( rc != X86EMUL_OKAY )
+ break;
rc = write_handler(v, p->addr + (sign * i * p->size), p->size,
data);
if ( rc != X86EMUL_OKAY )
@@ -165,8 +176,28 @@ static int process_portio_intercept(port
for ( i = 0; i < p->count; i++ )
{
data = 0;
- (void)hvm_copy_from_guest_phys(&data, p->data + sign*i*p->size,
- p->size);
+ switch ( hvm_copy_from_guest_phys(&data,
+ p->data + sign * i * p->size,
+ p->size) )
+ {
+ case HVMCOPY_okay:
+ break;
+ case HVMCOPY_gfn_paged_out:
+ case HVMCOPY_gfn_shared:
+ rc = X86EMUL_RETRY;
+ break;
+ case HVMCOPY_bad_gfn_to_mfn:
+ data = ~0;
+ break;
+ case HVMCOPY_bad_gva_to_gfn:
+ ASSERT(0);
+ /* fall through */
+ default:
+ rc = X86EMUL_UNHANDLEABLE;
+ break;
+ }
+ if ( rc != X86EMUL_OKAY )
+ break;
rc = action(IOREQ_WRITE, p->addr, p->size, &data);
if ( rc != X86EMUL_OKAY )
break;
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -340,14 +340,24 @@ static int dpci_ioport_write(uint32_t mp
data = p->data;
if ( p->data_is_ptr )
{
- int ret;
-
- ret = hvm_copy_from_guest_phys(&data,
- p->data + (sign * i * p->size),
- p->size);
- if ( (ret == HVMCOPY_gfn_paged_out) &&
- (ret == HVMCOPY_gfn_shared) )
+ switch ( hvm_copy_from_guest_phys(&data,
+ p->data + sign * i * p->size,
+ p->size) )
+ {
+ case HVMCOPY_okay:
+ break;
+ case HVMCOPY_gfn_paged_out:
+ case HVMCOPY_gfn_shared:
return X86EMUL_RETRY;
+ case HVMCOPY_bad_gfn_to_mfn:
+ data = ~0;
+ break;
+ case HVMCOPY_bad_gva_to_gfn:
+ ASSERT(0);
+ /* fall through */
+ default:
+ return X86EMUL_UNHANDLEABLE;
+ }
}
switch ( p->size )
--- a/xen/arch/x86/hvm/vmx/realmode.c
+++ b/xen/arch/x86/hvm/vmx/realmode.c
@@ -39,7 +39,9 @@ static void realmode_deliver_exception(
again:
last_byte = (vector * 4) + 3;
- if ( idtr->limit < last_byte )
+ if ( idtr->limit < last_byte ||
+ hvm_copy_from_guest_phys(&cs_eip, idtr->base + vector * 4, 4) !=
+ HVMCOPY_okay )
{
/* Software interrupt? */
if ( insn_len != 0 )
@@ -64,8 +66,6 @@ static void realmode_deliver_exception(
}
}
- (void)hvm_copy_from_guest_phys(&cs_eip, idtr->base + vector * 4, 4);
-
frame[0] = regs->eip + insn_len;
frame[1] = csr->sel;
frame[2] = regs->eflags & ~X86_EFLAGS_RF;
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