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[RFC,v2,09/18] livepatch/x86: add TIF_PATCH_PENDING thread flag

Message ID 6360fe5cab85aad424600518f645a9ac773cc72e.1461875890.git.jpoimboe@redhat.com (mailing list archive)
State Not Applicable
Headers show

Commit Message

Josh Poimboeuf April 28, 2016, 8:44 p.m. UTC 
Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
per-task consistency model for x86_64.  The bit getting set indicates
the thread has a pending patch which needs to be applied when the thread
exits the kernel.

The bit is placed in the least-significant word of the thread_info flags
so that it gets automatically included in the _TIF_ALLWORK_MASK macro.
This results in exit_to_usermode_loop() and klp_patch_task() getting
called when the bit is set.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/entry/common.c            | 9 ++++++---
 arch/x86/include/asm/thread_info.h | 2 ++
 2 files changed, 8 insertions(+), 3 deletions(-)

Comments

Andy Lutomirski April 29, 2016, 6:08 p.m. UTC | #1 
On Thu, Apr 28, 2016 at 1:44 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
> per-task consistency model for x86_64.  The bit getting set indicates
> the thread has a pending patch which needs to be applied when the thread
> exits the kernel.
>
> The bit is placed in the least-significant word of the thread_info flags

NAK to that part.

The least-significant word thing is a huge hack that has gotten out of
control.  Please add the thing explicitly to all relevant masks.

--Andy
Josh Poimboeuf April 29, 2016, 8:18 p.m. UTC | #2 
On Fri, Apr 29, 2016 at 11:08:04AM -0700, Andy Lutomirski wrote:
> On Thu, Apr 28, 2016 at 1:44 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
> > per-task consistency model for x86_64.  The bit getting set indicates
> > the thread has a pending patch which needs to be applied when the thread
> > exits the kernel.
> >
> > The bit is placed in the least-significant word of the thread_info flags
> 
> NAK to that part.
> 
> The least-significant word thing is a huge hack that has gotten out of
> control.  Please add the thing explicitly to all relevant masks.

Yeah, it is quite dangerous.  I'll make it explicit, and make all the
other _TIF_ALLWORK_MASK flags explicit while I'm at it.
diff mbox

Patch

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index ec138e5..0eaa1d9 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -21,6 +21,7 @@ 
 #include <linux/context_tracking.h>
 #include <linux/user-return-notifier.h>
 #include <linux/uprobes.h>
+#include <linux/livepatch.h>
 
 #include <asm/desc.h>
 #include <asm/traps.h>
@@ -202,14 +203,13 @@  long syscall_trace_enter(struct pt_regs *regs)
 
 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
-	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
+	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
 
 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 {
 	/*
 	 * In order to return to user mode, we need to have IRQs off with
-	 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
-	 * _TIF_UPROBE, or _TIF_NEED_RESCHED set.  Several of these flags
+	 * none of EXIT_TO_USERMODE_LOOP_FLAGS set.  Several of these flags
 	 * can be set at any time on preemptable kernels if we have IRQs on,
 	 * so we need to loop.  Disabling preemption wouldn't help: doing the
 	 * work to clear some of the flags can sleep.
@@ -236,6 +236,9 @@  static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 			fire_user_return_notifiers();
 
+		if (cached_flags & _TIF_PATCH_PENDING)
+			klp_patch_task(current);
+
 		/* Disable IRQs and retry */
 		local_irq_disable();
 
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 30c133a..4e4f50e 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -97,6 +97,7 @@  struct thread_info {
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_USER_RETURN_NOTIFY	11	/* notify kernel of userspace return */
 #define TIF_UPROBE		12	/* breakpointed or singlestepping */
+#define TIF_PATCH_PENDING	13	/* pending live patching update */
 #define TIF_NOTSC		16	/* TSC is not accessible in userland */
 #define TIF_IA32		17	/* IA32 compatibility process */
 #define TIF_FORK		18	/* ret_from_fork */
@@ -121,6 +122,7 @@  struct thread_info {
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_USER_RETURN_NOTIFY	(1 << TIF_USER_RETURN_NOTIFY)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
+#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)
 #define _TIF_NOTSC		(1 << TIF_NOTSC)
 #define _TIF_IA32		(1 << TIF_IA32)
 #define _TIF_FORK		(1 << TIF_FORK)