linux-kernel - [PATCH v3 18/19] x86/entry/64: Remove the SYSENTER stack canary

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <be3179c0a38c392fa44ebeb7dd89391ff5c010c3.1511497875.git.luto@kernel.org>
Date:   Thu, 23 Nov 2017 20:33:04 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     X86 ML <x86@...nel.org>
Cc:     Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v3 18/19] x86/entry/64: Remove the SYSENTER stack canary

Now that the SYSENTER stack has a guard page, there's no need for a
canary to detect overflow after the fact.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/processor.h | 1 -
 arch/x86/kernel/dumpstack.c      | 3 +--
 arch/x86/kernel/process.c        | 1 -
 arch/x86/kernel/traps.c          | 7 -------
 4 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 3a09e5571a92..7743aedb82ea 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -337,7 +337,6 @@ struct tss_struct {
 	 * Space for the temporary SYSENTER stack, used for SYSENTER
 	 * and the entry trampoline as well.
 	 */
-	unsigned long		SYSENTER_stack_canary;
 	unsigned long		SYSENTER_stack[64];
 
 	/*
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index bb61919c9335..9ce5fcf7d14d 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -48,8 +48,7 @@ bool in_sysenter_stack(unsigned long *stack, struct stack_info *info)
 	int cpu = smp_processor_id();
 	struct tss_struct *tss = &get_cpu_entry_area(cpu)->tss;
 
-	/* Treat the canary as part of the stack for unwinding purposes. */
-	void *begin = &tss->SYSENTER_stack_canary;
+	void *begin = &tss->SYSENTER_stack;
 	void *end = (void *)&tss->SYSENTER_stack + sizeof(tss->SYSENTER_stack);
 
 	if ((void *)stack < begin || (void *)stack >= end)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 86e83762e3b3..6a04287f222b 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -81,7 +81,6 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
 	  */
 	.io_bitmap		= { [0 ... IO_BITMAP_LONGS] = ~0 },
 #endif
-	.SYSENTER_stack_canary	= STACK_END_MAGIC,
 };
 EXPORT_PER_CPU_SYMBOL(cpu_tss);
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index cbc4272bb9dd..19475dbff068 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -801,13 +801,6 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 	debug_stack_usage_dec();
 
 exit:
-	/*
-	 * 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");
-
 	ist_exit(regs);
 }
 NOKPROBE_SYMBOL(do_debug);
-- 
2.13.6