The SYSENTER asm (32-bit and compat) contains fixups for regs->sp
and regs->flags. Move the fixups into C and fix some comments while
we're at it.
IMO this is a valid cleanup all by itself, and it also simplifies
the subsequent patch that will fix Xen PV SYSENTER.
Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
arch/x86/entry/common.c | 12 ++++++++++++
arch/x86/entry/entry_32.S | 5 ++---
arch/x86/entry/entry_64_compat.S | 11 +++++------
3 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index ed8ccc820995..f392a8bcd1c3 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -522,6 +522,18 @@ __visible noinstr long do_fast_syscall_32(struct pt_regs
*regs)
(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM))
== 0;
#endif
}
+
+/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
+__visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
+{
+ /* SYSENTER loses RSP, but the vDSO saved it in RBP. */
+ regs->sp = regs->bp;
+
+ /* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */
+ regs->flags |= X86_EFLAGS_IF;
+
+ return do_fast_syscall_32(regs);
+}
#endif
SYSCALL_DEFINE0(ni_syscall)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 024d7d276cd4..2d0bd5d5f032 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -933,9 +933,8 @@ SYM_FUNC_START(entry_SYSENTER_32)
.Lsysenter_past_esp:
pushl $__USER_DS /* pt_regs->ss */
- pushl %ebp /* pt_regs->sp (stashed in bp) */
+ pushl $0 /* pt_regs->sp (placeholder) */
pushfl /* pt_regs->flags (except IF = 0) */
- orl $X86_EFLAGS_IF, (%esp) /* Fix IF */
pushl $__USER_CS /* pt_regs->cs */
pushl $0 /* pt_regs->ip = 0 (placeholder) */
pushl %eax /* pt_regs->orig_ax */
@@ -965,7 +964,7 @@ SYM_FUNC_START(entry_SYSENTER_32)
.Lsysenter_flags_fixed:
movl %esp, %eax
- call do_fast_syscall_32
+ call do_SYSENTER_32
/* XEN PV guests always use IRET path */
ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
"jmp .Lsyscall_32_done", X86_FEATURE_XENPV
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 0f974ae01e62..7b9d8150f652 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -68,16 +68,15 @@ SYM_CODE_START(entry_SYSENTER_compat)
/* Construct struct pt_regs on stack */
pushq $__USER32_DS /* pt_regs->ss */
- pushq %rbp /* pt_regs->sp (stashed in bp) */
+ pushq $0 /* pt_regs->sp = 0 (placeholder) */
/*
* Push flags. This is nasty. First, interrupts are currently
- * off, but we need pt_regs->flags to have IF set. Second, even
- * if TF was set when SYSENTER started, it's clear by now. We fix
- * that later using TIF_SINGLESTEP.
+ * off, but we need pt_regs->flags to have IF set. Second, if TS
+ * was set in usermode, it's still set, and we're singlestepping
+ * through this code. do_SYSENTER_32() will fix up IF.
*/
pushfq /* pt_regs->flags (except IF = 0) */
- orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
pushq $__USER32_CS /* pt_regs->cs */
pushq $0 /* pt_regs->ip = 0 (placeholder) */
pushq %rax /* pt_regs->orig_ax */
@@ -135,7 +134,7 @@ SYM_CODE_START(entry_SYSENTER_compat)
.Lsysenter_flags_fixed:
movq %rsp, %rdi
- call do_fast_syscall_32
+ call do_SYSENTER_32
/* XEN PV guests always use IRET path */
ALTERNATIVE "testl %eax, %eax; jz
swapgs_restore_regs_and_return_to_usermode", \
"jmp swapgs_restore_regs_and_return_to_usermode",
X86_FEATURE_XENPV
--
2.25.4
