From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Mon, 4 Dec 2017 15:07:12 +0100
Subject: [PATCH] x86/entry/64: Allocate and enable the SYSENTER stack
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

CVE-2017-5754

This will simplify future changes that want scratch variables early in
the SYSENTER handler -- they'll be able to spill registers to the
stack.  It also lets us get rid of a SWAPGS_UNSAFE_STACK user.

This does not depend on CONFIG_IA32_EMULATION=y because we'll want the
stack space even without IA32 emulation.

As far as I can tell, the reason that this wasn't done from day 1 is
that we use IST for #DB and #BP, which is IMO rather nasty and causes
a lot more problems than it solves.  But, since #DB uses IST, we don't
actually need a real stack for SYSENTER (because SYSENTER with TF set
will invoke #DB on the IST stack rather than the SYSENTER stack).

I want to remove IST usage from these vectors some day, and this patch
is a prerequisite for that as well.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150605.312726423@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 1a79797b58cddfa948420a7553241c79c013e3ca)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
(cherry picked from commit 8e621515fa8d1649b031f34b9d498dcd865db1c3)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 arch/x86/include/asm/processor.h | 3 ---
 arch/x86/kernel/asm-offsets.c    | 5 +++++
 arch/x86/kernel/asm-offsets_32.c | 5 -----
 arch/x86/kernel/cpu/common.c     | 4 +++-
 arch/x86/kernel/process.c        | 2 --
 arch/x86/kernel/traps.c          | 3 +--
 arch/x86/entry/entry_64_compat.S | 2 +-
 7 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 79739e5f939a..5225917f9760 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -333,14 +333,11 @@ struct tss_struct {
 	 */
 	unsigned long		io_bitmap[IO_BITMAP_LONGS + 1];
 
-#ifdef CONFIG_X86_32
 	/*
 	 * Space for the temporary SYSENTER stack.
 	 */
 	unsigned long		SYSENTER_stack_canary;
 	unsigned long		SYSENTER_stack[64];
-#endif
-
 } ____cacheline_aligned;
 
 DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss);
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index de827d6ac8c2..031bd35bd911 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -92,4 +92,9 @@ void common(void) {
 
 	BLANK();
 	DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));
+
+	/* Offset from cpu_tss to SYSENTER_stack */
+	OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
+	/* Size of SYSENTER_stack */
+	DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
 }
diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index 880aa093268d..d09b161a3bd0 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -52,11 +52,6 @@ void foo(void)
 	DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) -
 	       offsetofend(struct tss_struct, SYSENTER_stack));
 
-	/* Offset from cpu_tss to SYSENTER_stack */
-	OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
-	/* Size of SYSENTER_stack */
-	DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
-
 #ifdef CONFIG_CC_STACKPROTECTOR
 	BLANK();
 	OFFSET(stack_canary_offset, stack_canary, canary);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 121fe3570d6f..aa97e4cd3a33 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1362,7 +1362,9 @@ void syscall_init(void)
 	 * AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
 	 */
 	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
-	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
+	wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
+		    (unsigned long)this_cpu_ptr(&cpu_tss) +
+		    offsetofend(struct tss_struct, SYSENTER_stack));
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
 #else
 	wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ccf3a4f4ef68..aa86e810fb54 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -70,9 +70,7 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
 	  */
 	.io_bitmap		= { [0 ... IO_BITMAP_LONGS] = ~0 },
 #endif
-#ifdef CONFIG_X86_32
 	.SYSENTER_stack_canary	= STACK_END_MAGIC,
-#endif
 };
 EXPORT_PER_CPU_SYMBOL(cpu_tss);
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3a46cab2696e..7b1d0df624cf 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -806,14 +806,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 	debug_stack_usage_dec();
 
 exit:
-#if defined(CONFIG_X86_32)
 	/*
 	 * This is the most likely code path that involves non-trivial use
 	 * of the SYSENTER stack.  Check that we haven't overrun it.
 	 */
 	WARN(this_cpu_read(cpu_tss.SYSENTER_stack_canary) != STACK_END_MAGIC,
 	     "Overran or corrupted SYSENTER stack\n");
-#endif
+
 	ist_exit(regs);
 }
 NOKPROBE_SYMBOL(do_debug);
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index be745b7a3e3e..1f76b66518ee 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -47,7 +47,7 @@
  */
 ENTRY(entry_SYSENTER_compat)
 	/* Interrupts are off on entry. */
-	SWAPGS_UNSAFE_STACK
+	SWAPGS
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
 	/*
-- 
2.14.2

