[PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths

Andy Lutomirski
2017-10-26T08:27:10Z

These code paths will diverge soon.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 32 +++++++++++++++++++++++---------
arch/x86/entry/entry_64_compat.S | 2 +-
arch/x86/kernel/head_64.S | 2 +-
3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index afe1f403fa0e..493e5e234d36 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -321,7 +321,7 @@ 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)
@@ -423,7 +423,7 @@ 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 */
@@ -612,7 +612,19 @@ 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
+ 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:
@@ -632,11 +644,13 @@ 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
+ testl $3, CS(%rsp)
+ jz 1f
+ ud2
+1:
+#endif
RESTORE_EXTRA_REGS
RESTORE_C_REGS
REMOVE_PT_GPREGS_FROM_STACK 8
@@ -1327,7 +1341,7 @@ 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:
/*
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index e26c25ca7756..9ca014a99968 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -337,7 +337,7 @@ 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)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 513cbb012ecc..0b01a105251b 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -326,7 +326,7 @@ early_idt_handler_common:

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

__INITDATA
--
2.13.6