linux-kernel - [PATCH 31/43] x86/mm/kaiser: Map entry stack variable

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Message-Id: <20171124172411.19476-32-mingo@kernel.org>
Date:   Fri, 24 Nov 2017 18:23:59 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 31/43] x86/mm/kaiser: Map entry stack variable

From: Dave Hansen <dave.hansen@...ux.intel.com>

There are times where the kernel is entered but there is no
safe stack, like at SYSCALL entry.  To obtain a safe stack, we
have to clobber %rsp and store the clobbered value in
'rsp_scratch'.

Map this to userspace to allow us to do this stack switch before
the CR3 switch.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: daniel.gruss@...k.tugraz.at
Cc: hughd@...gle.com
Cc: keescook@...gle.com
Cc: linux-mm@...ck.org
Cc: luto@...nel.org
Cc: michael.schwarz@...k.tugraz.at
Cc: moritz.lipp@...k.tugraz.at
Cc: richard.fellner@...dent.tugraz.at
Link: https://lkml.kernel.org/r/20171123003459.C0FF167A@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/process_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index bafe65b08697..9a0220aa2bf9 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -59,7 +59,7 @@
 #include <asm/unistd_32_ia32.h>
 #endif
 
-__visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
+__visible DEFINE_PER_CPU_USER_MAPPED(unsigned long, rsp_scratch);
 
 /* Prints also some state that isn't saved in the pt_regs */
 void __show_regs(struct pt_regs *regs, int all)
-- 
2.14.1