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

[Ingo Molnar]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: daniel.gruss@xxxxxxxxxxxxxx
Cc: hughd@xxxxxxxxxx
Cc: keescook@xxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: luto@xxxxxxxxxx
Cc: michael.schwarz@xxxxxxxxxxxxxx
Cc: moritz.lipp@xxxxxxxxxxxxxx
Cc: richard.fellner@xxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20171123003459.C0FF167A@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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