[patch 08/18] x86/syscall: Use [syscall_]enter_from_user_mode_randomize_stack()

[Thomas Gleixner]

These functions integrate the stack randomization.

syscall_enter_from_user_mode_randomize_stack() has the advantage that the
randomization happens early right after enter_from_user_mode().

In both cases also the overhead of get/put_cpu_var() in
add_random_kstack_offset() is avoided.

No functional change.

Signed-off-by: Thomas Gleixner <tglx at kernel.org>
Cc: x86 at kernel.org
---
 arch/x86/entry/syscall_32.c         |   19 +++++--------------
 arch/x86/entry/syscall_64.c         |    3 +--
 arch/x86/include/asm/entry-common.h |    1 -
 3 files changed, 6 insertions(+), 17 deletions(-)

--- a/arch/x86/entry/syscall_32.c
+++ b/arch/x86/entry/syscall_32.c
@@ -142,10 +142,9 @@ static __always_inline bool int80_is_ext
 	 * int80_is_external() below which calls into the APIC driver.
 	 * Identical for soft and external interrupts.
 	 */
-	enter_from_user_mode(regs);
+	enter_from_user_mode_randomize_stack(regs);
 
 	instrumentation_begin();
-	add_random_kstack_offset();
 
 	/* Validate that this is a soft interrupt to the extent possible */
 	if (unlikely(int80_is_external()))
@@ -210,11 +209,9 @@ DEFINE_FREDENTRY_RAW(int80_emulation)
 {
 	int nr;
 
-	enter_from_user_mode(regs);
+	enter_from_user_mode_randomize_stack(regs);
 
 	instrumentation_begin();
-	add_random_kstack_offset();
-
 	/*
 	 * FRED pushed 0 into regs::orig_ax and regs::ax contains the
 	 * syscall number.
@@ -252,10 +249,10 @@ DEFINE_FREDENTRY_RAW(int80_emulation)
 	 * orig_ax, the int return value truncates it. This matches
 	 * the semantics of syscall_get_nr().
 	 */
-	nr = syscall_enter_from_user_mode(regs, nr);
+	nr = syscall_enter_from_user_mode_randomize_stack(regs, nr);
+
 	instrumentation_begin();
 
-	add_random_kstack_offset();
 	do_syscall_32_irqs_on(regs, nr);
 
 	instrumentation_end();
@@ -268,15 +265,9 @@ static noinstr bool __do_fast_syscall_32
 	int nr = syscall_32_enter(regs);
 	int res;
 
-	/*
-	 * This cannot use syscall_enter_from_user_mode() as it has to
-	 * fetch EBP before invoking any of the syscall entry work
-	 * functions.
-	 */
-	enter_from_user_mode(regs);
+	enter_from_user_mode_randomize_stack(regs);
 
 	instrumentation_begin();
-	add_random_kstack_offset();
 	local_irq_enable();
 	/* Fetch EBP from where the vDSO stashed it. */
 	if (IS_ENABLED(CONFIG_X86_64)) {
--- a/arch/x86/entry/syscall_64.c
+++ b/arch/x86/entry/syscall_64.c
@@ -86,10 +86,9 @@ static __always_inline bool do_syscall_x
 /* Returns true to return using SYSRET, or false to use IRET */
 __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr)
 {
-	nr = syscall_enter_from_user_mode(regs, nr);
+	nr = syscall_enter_from_user_mode_randomize_stack(regs, nr);
 
 	instrumentation_begin();
-	add_random_kstack_offset();
 
 	if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
 		/* Invalid system call, but still a system call. */
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -2,7 +2,6 @@
 #ifndef _ASM_X86_ENTRY_COMMON_H
 #define _ASM_X86_ENTRY_COMMON_H
 
-#include <linux/randomize_kstack.h>
 #include <linux/user-return-notifier.h>
 
 #include <asm/nospec-branch.h>