3.2.101-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Dan Williams <dan.j.williams@xxxxxxxxx>
commit 085331dfc6bbe3501fb936e657331ca943827600 upstream.
Commit 75f139aaf896 "KVM: x86: Add memory barrier on vmcs field lookup"
added a raw 'asm("lfence");' to prevent a bounds check bypass of
'vmcs_field_to_offset_table'.
The lfence can be avoided in this path by using the array_index_nospec()
helper designed for these types of fixes.
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Andrew Honig <ahonig@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/151744959670.6342.3001723920950249067.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[bwh: Backported to 3.2:
- Replace max_vmcs_field with the local size variable
- Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -29,6 +29,7 @@
#include <linux/ftrace_event.h>
#include <linux/slab.h>
#include <linux/tboot.h>
+#include <linux/nospec.h>
#include "kvm_cache_regs.h"
#include "x86.h"
@@ -570,23 +571,21 @@ static unsigned short vmcs_field_to_offs
FIELD(HOST_RSP, host_rsp),
FIELD(HOST_RIP, host_rip),
};
-static const int max_vmcs_field = ARRAY_SIZE(vmcs_field_to_offset_table);
static inline short vmcs_field_to_offset(unsigned long field)
{
- if (field >= max_vmcs_field)
- return -1;
+ const size_t size = ARRAY_SIZE(vmcs_field_to_offset_table);
+ unsigned short offset;
- /*
- * FIXME: Mitigation for CVE-2017-5753. To be replaced with a
- * generic mechanism.
- */
- asm("lfence");
-
- if (vmcs_field_to_offset_table[field] == 0)
+ BUILD_BUG_ON(size > SHRT_MAX);
+ if (field >= size)
return -1;
- return vmcs_field_to_offset_table[field];
+ field = array_index_nospec(field, size);
+ offset = vmcs_field_to_offset_table[field];
+ if (offset == 0)
+ return -1;
+ return offset;
}
static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)
