x86/ldt: Disable 16-bit segments on Xen PV (cc801833) · Commits · 戴 / test

arch/x86/kernel/ldt.c

+34 −1

Original line number	Diff line number	Diff line
		@@ -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 +545,37 @@ 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()) {
		static DEFINE_MUTEX(xen_warning);
		static bool warned;

		mutex_lock(&xen_warning);
		if (!warned) {
		pr_info("Warning: 16-bit segments do not work correctly in a Xen PV guest\n");
		warned = true;
		}
		mutex_unlock(&xen_warning);

		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 +607,7 @@ 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;
		}