linux-kernel - [RFC PATCH v2 3/6] x86/pti: add a per-cpu variable pti

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Date:   Tue,  9 Jan 2018 13:56:17 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Willy Tarreau <w@....eu>, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>
Subject: [RFC PATCH v2 3/6] x86/pti: add a per-cpu variable pti_disable

This one is updated upon each context switch to reflect the
crrent mm's pti_disable field.

Signed-off-by: Willy Tarreau <w@....eu>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
---
 arch/x86/kernel/process_64.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9516310..9bb5908 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -61,6 +61,10 @@
 
 __visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
 
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+__visible DEFINE_PER_CPU(unsigned char, pti_disable);
+#endif
+
 /* Prints also some state that isn't saved in the pt_regs */
 void __show_regs(struct pt_regs *regs, int all)
 {
@@ -473,6 +477,11 @@ void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp)
 		     task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
 		__switch_to_xtra(prev_p, next_p, tss);
 
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+	this_cpu_write(pti_disable,
+		       next_p->mm && next_p->mm->context.pti_disable);
+#endif
+
 #ifdef CONFIG_XEN_PV
 	/*
 	 * On Xen PV, IOPL bits in pt_regs->flags have no effect, and
-- 
1.7.12.1