[PATCH 03/18] x86/asm/64: Move SWAPGS into the common iret-to-usermode path

Andy Lutomirski
2017-10-26T08:27:14Z

All of the code paths that ended up doing IRET to usermode did
SWAPGS immediately beforehand. Move the SWAPGS into the common
code.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 26 ++++++++++----------------
arch/x86/entry/entry_64_compat.S | 3 +--
2 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 493e5e234d36..1909a4e42b81 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -254,7 +254,7 @@ return_from_SYSCALL_64:
movq RCX(%rsp), %rcx
movq RIP(%rsp), %r11
cmpq %rcx, %r11 /* RCX == RIP */
- jne opportunistic_sysret_failed
+ jne swapgs_restore_regs_and_return_to_usermode

/*
* On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP
@@ -272,14 +272,14 @@ return_from_SYSCALL_64:

/* If this changed %rcx, it was not canonical */
cmpq %rcx, %r11
- jne opportunistic_sysret_failed
+ jne swapgs_restore_regs_and_return_to_usermode

cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */
- jne opportunistic_sysret_failed
+ jne swapgs_restore_regs_and_return_to_usermode

movq R11(%rsp), %r11
cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */
- jne opportunistic_sysret_failed
+ jne swapgs_restore_regs_and_return_to_usermode

/*
* SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot
@@ -300,12 +300,12 @@ return_from_SYSCALL_64:
* would never get past 'stuck_here'.
*/
testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
- jnz opportunistic_sysret_failed
+ jnz swapgs_restore_regs_and_return_to_usermode

/* nothing to check for RSP */

cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */
- jne opportunistic_sysret_failed
+ jne swapgs_restore_regs_and_return_to_usermode

/*
* We win! This label is here just for ease of understanding
@@ -318,10 +318,6 @@ syscall_return_via_sysret:
movq RSP(%rsp), %rsp
UNWIND_HINT_EMPTY
USERGS_SYSRET64
-
-opportunistic_sysret_failed:
- SWAPGS
- jmp restore_regs_and_return_to_usermode
END(entry_SYSCALL_64)

ENTRY(stub_ptregs_64)
@@ -422,8 +418,7 @@ ENTRY(ret_from_fork)
movq %rsp, %rdi
call syscall_return_slowpath /* returns with IRQs disabled */
TRACE_IRQS_ON /* user mode is traced as IRQS on */
- SWAPGS
- jmp restore_regs_and_return_to_usermode
+ jmp swapgs_restore_regs_and_return_to_usermode

1:
/* kernel thread */
@@ -611,15 +606,15 @@ GLOBAL(retint_user)
mov %rsp,%rdi
call prepare_exit_to_usermode
TRACE_IRQS_IRETQ
- SWAPGS

-GLOBAL(restore_regs_and_return_to_usermode)
+GLOBAL(swapgs_restore_regs_and_return_to_usermode)
#ifdef CONFIG_DEBUG_ENTRY
testl $3, CS(%rsp)
jnz 1f
ud2
1:
#endif
+ SWAPGS
RESTORE_EXTRA_REGS
RESTORE_C_REGS
REMOVE_PT_GPREGS_FROM_STACK 8
@@ -1340,8 +1335,7 @@ ENTRY(nmi)
* Return back to user mode. We must *not* do the normal exit
* work, because we don't want to enable interrupts.
*/
- SWAPGS
- jmp restore_regs_and_return_to_usermode
+ jmp swapgs_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 9ca014a99968..932b96ce1b06 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -336,8 +336,7 @@ ENTRY(entry_INT80_compat)

/* Go back to user mode. */
TRACE_IRQS_ON
- SWAPGS
- jmp restore_regs_and_return_to_usermode
+ jmp swapgs_restore_regs_and_return_to_usermode
END(entry_INT80_compat)

ENTRY(stub32_clone)
--
2.13.6