[PATCH 4.14 036/159] x86/entry/64: Split the IRET-to-user and IRET-to-kernel paths

Greg Kroah-Hartman
2017-12-22T08:59:54Z

From: Andy Lutomirski <luto@kernel.org>

commit 26c4ef9c49d8a0341f6d97ce2cfdd55d1236ed29 upstream.

These code paths will diverge soon.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/dccf8c7b3750199b4b30383c812d4e2931811509.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/entry/entry_64.S | 34 +++++++++++++++++++++++++---------
arch/x86/entry/entry_64_compat.S | 2 +-
arch/x86/kernel/head_64.S | 2 +-
3 files changed, 27 insertions(+), 11 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -322,7 +322,7 @@ syscall_return_via_sysret:

opportunistic_sysret_failed:
SWAPGS
- jmp restore_regs_and_iret
+ jmp restore_regs_and_return_to_usermode
END(entry_SYSCALL_64)

ENTRY(stub_ptregs_64)
@@ -424,7 +424,7 @@ ENTRY(ret_from_fork)
call syscall_return_slowpath /* returns with IRQs disabled */
TRACE_IRQS_ON /* user mode is traced as IRQS on */
SWAPGS
- jmp restore_regs_and_iret
+ jmp restore_regs_and_return_to_usermode

1:
/* kernel thread */
@@ -613,7 +613,20 @@ GLOBAL(retint_user)
call prepare_exit_to_usermode
TRACE_IRQS_IRETQ
SWAPGS
- jmp restore_regs_and_iret
+
+GLOBAL(restore_regs_and_return_to_usermode)
+#ifdef CONFIG_DEBUG_ENTRY
+ /* Assert that pt_regs indicates user mode. */
+ testl $3, CS(%rsp)
+ jnz 1f
+ ud2
+1:
+#endif
+ RESTORE_EXTRA_REGS
+ RESTORE_C_REGS
+ REMOVE_PT_GPREGS_FROM_STACK 8
+ INTERRUPT_RETURN
+

/* Returning to kernel space */
retint_kernel:
@@ -633,11 +646,14 @@ retint_kernel:
*/
TRACE_IRQS_IRETQ

-/*
- * At this label, code paths which return to kernel and to user,
- * which come from interrupts/exception and from syscalls, merge.
- */
-GLOBAL(restore_regs_and_iret)
+GLOBAL(restore_regs_and_return_to_kernel)
+#ifdef CONFIG_DEBUG_ENTRY
+ /* Assert that pt_regs indicates kernel mode. */
+ testl $3, CS(%rsp)
+ jz 1f
+ ud2
+1:
+#endif
RESTORE_EXTRA_REGS
RESTORE_C_REGS
REMOVE_PT_GPREGS_FROM_STACK 8
@@ -1328,7 +1344,7 @@ ENTRY(nmi)
* work, because we don't want to enable interrupts.
*/
SWAPGS
- jmp restore_regs_and_iret
+ jmp restore_regs_and_return_to_usermode

.Lnmi_from_kernel:
/*
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -338,7 +338,7 @@ ENTRY(entry_INT80_compat)
/* Go back to user mode. */
TRACE_IRQS_ON
SWAPGS
- jmp restore_regs_and_iret
+ jmp restore_regs_and_return_to_usermode
END(entry_INT80_compat)

ENTRY(stub32_clone)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -328,7 +328,7 @@ early_idt_handler_common:

20:
decl early_recursion_flag(%rip)
- jmp restore_regs_and_iret
+ jmp restore_regs_and_return_to_kernel
END(early_idt_handler_common)

__INITDATA