Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Ingo Molnar:
 "Various fixes:

   - Fix the PAT performance regression that downgraded write-combining
     device memory regions to uncached.

   - There's been a number of bugs in 32-bit double fault handling -
     hopefully all fixed now.

   - Fix an LDT crash

   - Fix an FPU over-optimization that broke with GCC9 code
     optimizations.

   - Misc cleanups"

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/mm/pat: Fix off-by-one bugs in interval tree search
  x86/ioperm: Save an indentation level in tss_update_io_bitmap()
  x86/fpu: Don't cache access to fpu_fpregs_owner_ctx
  x86/entry/32: Remove unused 'restore_all_notrace' local label
  x86/ptrace: Document FSBASE and GSBASE ABI oddities
  x86/ptrace: Remove set_segment_reg() implementations for current
  x86/traps: die() instead of panicking on a double fault
  x86/doublefault/32: Rewrite the x86_32 #DF handler and unify with 64-bit
  x86/doublefault/32: Move #DF stack and TSS to cpu_entry_area
  x86/doublefault/32: Rename doublefault.c to doublefault_32.c
  x86/traps: Disentangle the 32-bit and 64-bit doublefault code
  lkdtm: Add a DOUBLE_FAULT crash type on x86
  selftests/x86/single_step_syscall: Check SYSENTER directly
  x86/mm/32: Sync only to VMALLOC_END in vmalloc_sync_all()

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 7284a22b1a09..a4fdad04809a 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -12,6 +12,10 @@
 #include <linux/sched/task_stack.h>
 #include <linux/uaccess.h>
 
+#ifdef CONFIG_X86_32
+#include <asm/desc.h>
+#endif
+
 struct lkdtm_list {
 	struct list_head node;
 };
@@ -337,3 +341,38 @@ void lkdtm_UNSET_SMEP(void)
 	pr_err("FAIL: this test is x86_64-only\n");
 #endif
 }
+
+#ifdef CONFIG_X86_32
+void lkdtm_DOUBLE_FAULT(void)
+{
+	/*
+	 * Trigger #DF by setting the stack limit to zero.  This clobbers
+	 * a GDT TLS slot, which is okay because the current task will die
+	 * anyway due to the double fault.
+	 */
+	struct desc_struct d = {
+		.type = 3,	/* expand-up, writable, accessed data */
+		.p = 1,		/* present */
+		.d = 1,		/* 32-bit */
+		.g = 0,		/* limit in bytes */
+		.s = 1,		/* not system */
+	};
+
+	local_irq_disable();
+	write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()),
+			GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S);
+
+	/*
+	 * Put our zero-limit segment in SS and then trigger a fault.  The
+	 * 4-byte access to (%esp) will fault with #SS, and the attempt to
+	 * deliver the fault will recursively cause #SS and result in #DF.
+	 * This whole process happens while NMIs and MCEs are blocked by the
+	 * MOV SS window.  This is nice because an NMI with an invalid SS
+	 * would also double-fault, resulting in the NMI or MCE being lost.
+	 */
+	asm volatile ("movw %0, %%ss; addl $0, (%%esp)" ::
+		      "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3)));
+
+	panic("tried to double fault but didn't die\n");
+}
+#endif