Yet another KPTI fix

kernel.spec

@@ -42,7 +42,7 @@ Summary: The Linux kernel
 # For non-released -rc kernels, this will be appended after the rcX and
 # gitX tags, so a 3 here would become part of release "0.rcX.gitX.3"
 #
-%global baserelease 2
+%global baserelease 3
 %global fedora_build %{baserelease}
 
 # base_sublevel is the kernel version we're starting with and patching
@@ -2201,6 +2201,9 @@ fi
 #
 #
 %changelog
+* Wed Jan 03 2018 Laura Abbott <labbott@redhat.com> - 4.15.0-0.rc6.git0.3
+- Yet another KPTI fix
+
 * Wed Jan 03 2018 Laura Abbott <labbott@redhat.com> - 4.15.0-0.rc6.git0.2
 - KPTI Fix
 

kpti-fix.patch

@@ -54,3 +54,76 @@ index bce8aea..2da28ba 100644
 -- 
 cgit v1.1
 
+From fea692ec9308084475c0c93bf74bcb2a35f3d417 Mon Sep 17 00:00:00 2001
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Wed, 3 Jan 2018 19:52:04 +0100
+Subject: [PATCH] CONFIG_PAGE_TABLE_ISOLATION=y on x86_64 causes gcc to
+ segfault when building x86_32 binaries
+
+On Wed, 3 Jan 2018, Thomas Gleixner wrote:
+
+> On Wed, 3 Jan 2018, Lars Wendler wrote:
+> > Am Wed, 3 Jan 2018 13:05:38 +0100 (CET)
+> > schrieb Thomas Gleixner <tglx@linutronix.de>:
+> > > Also can you please try Linus v4.15-rc6 with PTI enabled so we can see
+> > > whether that's a backport issue or a general one?
+> >
+> > Same problem with 4.15-rc6. So I suppose that means it's a general
+> > issue.
+>
+> Just a shot in the dark as I just decoded another issue on a AMD CPU. Can
+> you please try the patch below?
+
+Ok. Found the real issue. This is a problem on AMD boxen.
+
+Fix below.
+
+Can Xen folks please have a look at that as well?
+
+Thanks,
+
+	tglx
+
+8<-------------------
+
+arch/x86/entry/entry_64_compat.S |   13 ++++++-------
+ 1 file changed, 6 insertions(+), 7 deletions(-)
+---
+ arch/x86/entry/entry_64_compat.S | 13 ++++++-------
+ 1 file changed, 6 insertions(+), 7 deletions(-)
+
+diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
+index 40f17009ec20..4c4b9545b848 100644
+--- a/arch/x86/entry/entry_64_compat.S
++++ b/arch/x86/entry/entry_64_compat.S
+@@ -190,8 +190,13 @@ ENTRY(entry_SYSCALL_compat)
+ 	/* Interrupts are off on entry. */
+ 	swapgs
+ 
+-	/* Stash user ESP and switch to the kernel stack. */
++	/* Stash user ESP */
+ 	movl	%esp, %r8d
++
++	/* Use %rsp as scratch reg. User ESP is stashed in r8 */
++	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
++	
++	/* Switch to the kernel stack */
+ 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
+ 
+ 	/* Construct struct pt_regs on stack */
+@@ -219,12 +224,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
+ 	pushq   $0			/* pt_regs->r14 = 0 */
+ 	pushq   $0			/* pt_regs->r15 = 0 */
+ 
+-	/*
+-	 * We just saved %rdi so it is safe to clobber.  It is not
+-	 * preserved during the C calls inside TRACE_IRQS_OFF anyway.
+-	 */
+-	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
+-
+ 	/*
+ 	 * User mode is traced as though IRQs are on, and SYSENTER
+ 	 * turned them off.
+-- 
+2.14.3
+