* [PATCH 1/2] x86/entry/64: Rearrange SYSCALL entry points for Xen's benefit
2015-07-26 23:29 [PATCH 0/2] x86_64, xen: Simplify Xen SYSCALL handling Andy Lutomirski
@ 2015-07-26 23:29 ` Andy Lutomirski
2015-07-26 23:29 ` [PATCH 2/2] x86/xen/64: Rearrange the SYSCALL entries Andy Lutomirski
1 sibling, 0 replies; 3+ messages in thread
From: Andy Lutomirski @ 2015-07-26 23:29 UTC (permalink / raw)
To: X86 ML, xen-devel, Andrew Cooper
Cc: Boris Ostrovsky, linux-kernel, Borislav Petkov, Steven Rostedt,
Andy Lutomirski
Xen currently fudges RSP on SYSCALL to be compatible with the native
entries. This has the unfortunate side effect that there are extra
poorly-controlled places with user RSP. Add better entry points for
Xen to use instead.
This will add a couple of cycles of IRQ latency, but it avoids an
annoying corner case in which an IRQ can be delivered with a
hardware frame that overlaps current_pt_regs.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 20 ++++++++++++++------
arch/x86/entry/entry_64_compat.S | 10 ++++++----
2 files changed, 20 insertions(+), 10 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 041a37a643e1..f47996910331 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -148,17 +148,19 @@ GLOBAL(entry_SYSCALL_64_after_swapgs)
/* Construct struct pt_regs on stack */
pushq $__USER_DS /* pt_regs->ss */
pushq PER_CPU_VAR(rsp_scratch) /* pt_regs->sp */
+
/*
- * Re-enable interrupts.
- * We use 'rsp_scratch' as a scratch space, hence irq-off block above
- * must execute atomically in the face of possible interrupt-driven
- * task preemption. We must enable interrupts only after we're done
- * with using rsp_scratch:
+ * Before this point, interrupts MUST be off to prevent rsp_scratch
+ * from getting corrupted due to preemption. Nonetheless, we keep
+ * interrupts off a little longer. We eventually want to make it
+ * all the way to C code with interrupts off, which will considerably
+ * simplify context tracking.
*/
- ENABLE_INTERRUPTS(CLBR_NONE)
+
pushq %r11 /* pt_regs->flags */
pushq $__USER_CS /* pt_regs->cs */
pushq %rcx /* pt_regs->ip */
+GLOBAL(entry_SYSCALL_64_after_hwframe)
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
@@ -171,6 +173,12 @@ GLOBAL(entry_SYSCALL_64_after_swapgs)
pushq %r11 /* pt_regs->r11 */
sub $(6*8), %rsp /* pt_regs->bp, bx, r12-15 not saved */
+ /*
+ * Re-enable interrupts. IRQ tracing already thinks they're
+ * on because user mode is traced as IRQs-on.
+ */
+ ENABLE_INTERRUPTS(CLBR_NONE)
+
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
jnz tracesys
entry_SYSCALL_64_fastpath:
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index d7571532e7ce..d39495d6446e 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -312,10 +312,6 @@ ENTRY(entry_SYSCALL_compat)
SWAPGS_UNSAFE_STACK
movl %esp, %r8d
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
- ENABLE_INTERRUPTS(CLBR_NONE)
-
- /* Zero-extending 32-bit regs, do not remove */
- movl %eax, %eax
/* Construct struct pt_regs on stack */
pushq $__USER32_DS /* pt_regs->ss */
@@ -323,6 +319,7 @@ ENTRY(entry_SYSCALL_compat)
pushq %r11 /* pt_regs->flags */
pushq $__USER32_CS /* pt_regs->cs */
pushq %rcx /* pt_regs->ip */
+GLOBAL(entry_SYSCALL_compat_after_hwframe_esp_in_r8d)
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
@@ -332,6 +329,11 @@ ENTRY(entry_SYSCALL_compat)
pushq $-ENOSYS /* pt_regs->ax */
sub $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */
+ ENABLE_INTERRUPTS(CLBR_NONE)
+
+ /* Zero-extending 32-bit regs, do not remove */
+ movl %eax, %eax
+
/*
* No need to do an access_ok check here because r8 has been
* 32-bit zero extended:
--
2.4.3
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH 2/2] x86/xen/64: Rearrange the SYSCALL entries
2015-07-26 23:29 [PATCH 0/2] x86_64, xen: Simplify Xen SYSCALL handling Andy Lutomirski
2015-07-26 23:29 ` [PATCH 1/2] x86/entry/64: Rearrange SYSCALL entry points for Xen's benefit Andy Lutomirski
@ 2015-07-26 23:29 ` Andy Lutomirski
1 sibling, 0 replies; 3+ messages in thread
From: Andy Lutomirski @ 2015-07-26 23:29 UTC (permalink / raw)
To: X86 ML, xen-devel, Andrew Cooper
Cc: Boris Ostrovsky, linux-kernel, Borislav Petkov, Steven Rostedt,
Andy Lutomirski
Xen's raw SYSCALL entries are much less weird than native. Rather
than fudging them to look like native entries, use the Xen-provided
stack frame directly.
This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses
of the SWAPGS_UNSAFE_STACK paravirt hook.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 9 +--------
arch/x86/entry/entry_64_compat.S | 2 +-
arch/x86/xen/xen-asm_64.S | 24 ++++++++++--------------
3 files changed, 12 insertions(+), 23 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f47996910331..ebe7e2ca19fe 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -134,14 +134,7 @@ ENTRY(entry_SYSCALL_64)
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
* it is too small to ever cause noticeable irq latency.
*/
- SWAPGS_UNSAFE_STACK
- /*
- * A hypervisor implementation might want to use a label
- * after the swapgs, so that it can do the swapgs
- * for the guest and jump here on syscall.
- */
-GLOBAL(entry_SYSCALL_64_after_swapgs)
-
+ swapgs
movq %rsp, PER_CPU_VAR(rsp_scratch)
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index d39495d6446e..beae2b75b588 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -309,7 +309,7 @@ ENTRY(entry_SYSCALL_compat)
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
* it is too small to ever cause noticeable irq latency.
*/
- SWAPGS_UNSAFE_STACK
+ swapgs
movl %esp, %r8d
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index f22667abf7b9..c2b5868a9967 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -100,34 +100,30 @@ RELOC(xen_sysret32, 1b+1)
* rip
* r11
* rsp->rcx
- *
- * In all the entrypoints, we undo all that to make it look like a
- * CPU-generated syscall/sysenter and jump to the normal entrypoint.
*/
-.macro undo_xen_syscall
- mov 0*8(%rsp), %rcx
- mov 1*8(%rsp), %r11
- mov 5*8(%rsp), %rsp
-.endm
-
/* Normal 64-bit system call target */
ENTRY(xen_syscall_target)
- undo_xen_syscall
- jmp entry_SYSCALL_64_after_swapgs
+ popq %rcx
+ popq %r11
+ jmp entry_SYSCALL_64_after_hwframe
ENDPROC(xen_syscall_target)
#ifdef CONFIG_IA32_EMULATION
/* 32-bit compat syscall target */
ENTRY(xen_syscall32_target)
- undo_xen_syscall
- jmp entry_SYSCALL_compat
+ popq %rcx
+ popq %r11
+ movl (3*8)(%rsp), %r8d /* r8d = user esp */
+ jmp entry_SYSCALL_compat_after_hwframe_esp_in_r8d
ENDPROC(xen_syscall32_target)
/* 32-bit compat sysenter target */
ENTRY(xen_sysenter_target)
- undo_xen_syscall
+ mov 0*8(%rsp), %rcx
+ mov 1*8(%rsp), %r11
+ mov 5*8(%rsp), %rsp
jmp entry_SYSENTER_compat
ENDPROC(xen_sysenter_target)
--
2.4.3
^ permalink raw reply [flat|nested] 3+ messages in thread