[PATCH 34 of 36] x86_64: swapgs pvop with a user-stack can never be called

Jeremy Fitzhardinge
2008-06-25T04:43:59Z

It's never safe to call a swapgs pvop when the user stack is current -
it must be inline replaced. Rather than making a call, the
SWAPGS_UNSAFE_STACK pvop always just puts "swapgs" as a placeholder,
which must either be replaced inline or trap'n'emulated (somehow).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
include/asm-x86/irqflags.h | 2 +-
include/asm-x86/paravirt.h | 10 ++++++++++
2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/asm-x86/irqflags.h b/include/asm-x86/irqflags.h
--- a/include/asm-x86/irqflags.h
+++ b/include/asm-x86/irqflags.h
@@ -167,6 +167,7 @@
#define INTERRUPT_RETURN_NMI_SAFE NATIVE_INTERRUPT_RETURN_NMI_SAFE

#ifdef CONFIG_X86_64
+#define SWAPGS_UNSAFE_STACK swapgs
#define INTERRUPT_RETURN iretq
#define USERGS_SYSRET64 \
swapgs; \
@@ -241,7 +242,6 @@
* Either way, this is a good way to document that we don't
* have a reliable stack. x86_64 only.
*/
-#define SWAPGS_UNSAFE_STACK swapgs
#define ARCH_LOCKDEP_SYS_EXIT call lockdep_sys_exit_thunk
#define ARCH_LOCKDEP_SYS_EXIT_IRQ \
TRACE_IRQS_ON; \
diff --git a/include/asm-x86/paravirt.h b/include/asm-x86/paravirt.h
--- a/include/asm-x86/paravirt.h
+++ b/include/asm-x86/paravirt.h
@@ -1529,6 +1529,16 @@

#else /* !CONFIG_X86_32 */
+
+/*
+ * If swapgs is used while the userspace stack is still current,
+ * there's no way to call a pvop. The PV replacement *must* be
+ * inlined, or the swapgs instruction must be trapped and emulated.
+ */
+#define SWAPGS_UNSAFE_STACK \
+ PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE, \
+ swapgs)
+
#define SWAPGS \
PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE, \
PV_SAVE_REGS; \