linux-kernel - [tip:x86/asm] x86/asm/entry: Delay loading sp0 slightly on task switch

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]

Date:	Sat, 7 Mar 2015 00:37:25 -0800
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	luto@...capital.net, linux-kernel@...r.kernel.org, oleg@...hat.com,
	mingo@...nel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, dvlasenk@...hat.com, hpa@...or.com,
	bp@...en8.de
Subject: [tip:x86/asm] x86/asm/entry:
  Delay loading sp0 slightly on task switch

Commit-ID:  b27559a433bb6080d95c2593d4a2b81401197911
Gitweb:     http://git.kernel.org/tip/b27559a433bb6080d95c2593d4a2b81401197911
Author:     Andy Lutomirski <luto@...capital.net>
AuthorDate: Fri, 6 Mar 2015 17:50:18 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 7 Mar 2015 09:34:03 +0100

x86/asm/entry: Delay loading sp0 slightly on task switch

The change:

  75182b1632a8 ("x86/asm/entry: Switch all C consumers of kernel_stack to this_cpu_sp0()")

had the unintended side effect of changing the return value of
current_thread_info() during part of the context switch process.
Change it back.

This has no effect as far as I can tell -- it's just for
consistency.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/9fcaa47dd8487db59eed7a3911b6ae409476763e.1425692936.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/process_32.c | 10 +++++-----
 arch/x86/kernel/process_64.c |  6 +++---
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d3460af..0405cab 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -256,11 +256,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	fpu = switch_fpu_prepare(prev_p, next_p, cpu);
 
 	/*
-	 * Reload esp0.
-	 */
-	load_sp0(tss, next);
-
-	/*
 	 * Save away %gs. No need to save %fs, as it was saved on the
 	 * stack on entry.  No need to save %es and %ds, as those are
 	 * always kernel segments while inside the kernel.  Doing this
@@ -310,6 +305,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	 */
 	arch_end_context_switch(next_p);
 
+	/*
+	 * Reload esp0.  This changes current_thread_info().
+	 */
+	load_sp0(tss, next);
+
 	this_cpu_write(kernel_stack,
 		  (unsigned long)task_stack_page(next_p) +
 		  THREAD_SIZE - KERNEL_STACK_OFFSET);
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 2cd562f..1e393d2 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -283,9 +283,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	fpu = switch_fpu_prepare(prev_p, next_p, cpu);
 
-	/* Reload esp0 and ss1. */
-	load_sp0(tss, next);
-
 	/* We must save %fs and %gs before load_TLS() because
 	 * %fs and %gs may be cleared by load_TLS().
 	 *
@@ -413,6 +410,9 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	task_thread_info(prev_p)->saved_preempt_count = this_cpu_read(__preempt_count);
 	this_cpu_write(__preempt_count, task_thread_info(next_p)->saved_preempt_count);
 
+	/* Reload esp0 and ss1.  This changes current_thread_info(). */
+	load_sp0(tss, next);
+
 	this_cpu_write(kernel_stack,
 		  (unsigned long)task_stack_page(next_p) +
 		  THREAD_SIZE - KERNEL_STACK_OFFSET);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/