summaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/ldt.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kernel/ldt.c')
-rw-r--r--arch/x86/kernel/ldt.c26
1 files changed, 25 insertions, 1 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index 8748321c4486..b8aee71840ae 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -29,6 +29,8 @@
#include <asm/mmu_context.h>
#include <asm/pgtable_areas.h>
+#include <xen/xen.h>
+
/* This is a multiple of PAGE_SIZE. */
#define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
@@ -543,6 +545,28 @@ static int read_default_ldt(void __user *ptr, unsigned long bytecount)
return bytecount;
}
+static bool allow_16bit_segments(void)
+{
+ if (!IS_ENABLED(CONFIG_X86_16BIT))
+ return false;
+
+#ifdef CONFIG_XEN_PV
+ /*
+ * Xen PV does not implement ESPFIX64, which means that 16-bit
+ * segments will not work correctly. Until either Xen PV implements
+ * ESPFIX64 and can signal this fact to the guest or unless someone
+ * provides compelling evidence that allowing broken 16-bit segments
+ * is worthwhile, disallow 16-bit segments under Xen PV.
+ */
+ if (xen_pv_domain()) {
+ pr_info_once("Warning: 16-bit segments do not work correctly in a Xen PV guest\n");
+ return false;
+ }
+#endif
+
+ return true;
+}
+
static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
{
struct mm_struct *mm = current->mm;
@@ -574,7 +598,7 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
/* The user wants to clear the entry. */
memset(&ldt, 0, sizeof(ldt));
} else {
- if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
+ if (!ldt_info.seg_32bit && !allow_16bit_segments()) {
error = -EINVAL;
goto out;
}