linux-kernel - [PATCH 15/30] x86, kaiser: map entry stack variables

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Message-Id: <20171108194715.3292DBFB@viggo.jf.intel.com>
Date:   Wed, 08 Nov 2017 11:47:15 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, dave.hansen@...ux.intel.com,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        luto@...nel.org, torvalds@...ux-foundation.org,
        keescook@...gle.com, hughd@...gle.com, x86@...nel.org
Subject: [PATCH 15/30] x86, kaiser: map entry stack variables


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

There are times that we enter the kernel and do not have a safe
stack, like at SYSCALL entry.  We use the per-cpu vairables
'rsp_scratch' and 'cpu_current_top_of_stack' to save off the old
%rsp and find a safe place to have a stack.

You can not directly manipulate the CR3 register.  You can only
'MOV' to it from another register, which means we need to clobber
a register in order to do any CR3 manipulation.  User-mapping these
variables allows us to obtain a safe stack *before* we switch the
CR3 value.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Moritz Lipp <moritz.lipp@...k.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@...k.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@...k.tugraz.at>
Cc: Richard Fellner <richard.fellner@...dent.tugraz.at>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...gle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: x86@...nel.org
---

 b/arch/x86/kernel/cpu/common.c |    2 +-
 b/arch/x86/kernel/process_64.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff -puN arch/x86/kernel/cpu/common.c~kaiser-user-map-stack-helper-vars arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~kaiser-user-map-stack-helper-vars	2017-11-08 10:45:34.001681383 -0800
+++ b/arch/x86/kernel/cpu/common.c	2017-11-08 10:45:34.007681383 -0800
@@ -1447,7 +1447,7 @@ DEFINE_PER_CPU_ALIGNED(struct stack_cana
  * trampoline, not the thread stack.  Use an extra percpu variable to track
  * the top of the kernel stack directly.
  */
-DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) =
+DEFINE_PER_CPU_USER_MAPPED(unsigned long, cpu_current_top_of_stack) =
 	(unsigned long)&init_thread_union + THREAD_SIZE;
 EXPORT_PER_CPU_SYMBOL(cpu_current_top_of_stack);
 
diff -puN arch/x86/kernel/process_64.c~kaiser-user-map-stack-helper-vars arch/x86/kernel/process_64.c
--- a/arch/x86/kernel/process_64.c~kaiser-user-map-stack-helper-vars	2017-11-08 10:45:34.003681383 -0800
+++ b/arch/x86/kernel/process_64.c	2017-11-08 10:45:34.007681383 -0800
@@ -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)
_