From: "tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Brian Gerst <brgerst@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Daniel Thompson <daniel.thompson@linaro.org>,
x86 <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/entry] x86/debug: Remove the historical junk
Date: Fri, 04 Sep 2020 13:16:08 -0000 [thread overview]
Message-ID: <159922536806.20229.4215385228775090226.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200902133201.170216274@infradead.org>
The following commit has been merged into the x86/entry branch of tip:
Commit-ID: 389cd0cd8b3790b555c3679da946f4aa4fba3bab
Gitweb: https://git.kernel.org/tip/389cd0cd8b3790b555c3679da946f4aa4fba3bab
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 02 Sep 2020 15:25:58 +02:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 04 Sep 2020 15:12:55 +02:00
x86/debug: Remove the historical junk
Remove the historical junk and replace it with a WARN and a comment.
The problem is that even though the kernel only uses TF single-step in
kprobes and KGDB, both of which consume the event before this, QEMU/KVM has
bugs in this area that can trigger this state so it has to be dealt with.
Suggested-by: Brian Gerst <brgerst@gmail.com>
Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200902133201.170216274@infradead.org
---
arch/x86/kernel/traps.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 682af24..1e89001 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -843,18 +843,19 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
if (notify_debug(regs, &dr6))
goto out;
- if (WARN_ON_ONCE(dr6 & DR_STEP)) {
- /*
- * Historical junk that used to handle SYSENTER single-stepping.
- * This should be unreachable now. If we survive for a while
- * without anyone hitting this warning, we'll turn this into
- * an oops.
- */
- dr6 &= ~DR_STEP;
- set_thread_flag(TIF_SINGLESTEP);
+ /*
+ * The kernel doesn't use TF single-step outside of:
+ *
+ * - Kprobes, consumed through kprobe_debug_handler()
+ * - KGDB, consumed through notify_debug()
+ *
+ * So if we get here with DR_STEP set, something is wonky.
+ *
+ * A known way to trigger this is through QEMU's GDB stub,
+ * which leaks #DB into the guest and causes IST recursion.
+ */
+ if (WARN_ON_ONCE(current->thread.debugreg6 & DR_STEP))
regs->flags &= ~X86_EFLAGS_TF;
- }
-
out:
instrumentation_end();
idtentry_exit_nmi(regs, irq_state);
next prev parent reply other threads:[~2020-09-04 13:20 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 13:25 [PATCH 00/13] x86/debug: Untangle handle_debug() Peter Zijlstra
2020-09-02 13:25 ` [PATCH 01/13] x86/entry: Fix AC assertion Peter Zijlstra
2020-09-02 15:58 ` Brian Gerst
2020-09-02 16:24 ` Jürgen Groß
2020-09-02 16:31 ` peterz
2020-09-02 17:02 ` Brian Gerst
2020-09-02 16:26 ` Andrew Cooper
2020-09-04 13:16 ` [tip: x86/urgent] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 02/13] x86/debug: Allow a single level of #DB recursion Peter Zijlstra
2020-09-02 23:59 ` Sasha Levin
2020-09-03 16:12 ` Josh Poimboeuf
2020-09-02 13:25 ` [PATCH 03/13] x86/debug: Sync BTF earlier Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 04/13] x86/debug: Move kprobe_debug_handler() into exc_debug_kernel() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 05/13] x86/debug: Remove handle_debug(.user) argument Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 06/13] x86/debug: Simplify #DB signal code Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 07/13] x86/debug: Move historical SYSENTER junk into exc_debug_kernel() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 08/13] x86/debug: Move cond_local_irq_enable() block into exc_debug_user() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:25 ` [PATCH 09/13] x86/debug: Remove the historical junk Peter Zijlstra
2020-09-04 13:16 ` tip-bot2 for Peter Zijlstra [this message]
2020-09-02 13:25 ` [PATCH 10/13] x86/debug: Remove aout_dump_debugregs() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:26 ` [PATCH 11/13] x86/debug: Simplify hw_breakpoint_handler() Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:26 ` [RFC][PATCH 12/13] x86/debug: Support negative polarity DR6 bits Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-02 13:26 ` [RFC][PATCH 13/13] x86/debug: Change thread.debugreg6 to thread.virtual_dr6 Peter Zijlstra
2020-09-04 13:16 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-09-03 15:21 ` [PATCH 00/13] x86/debug: Untangle handle_debug() Daniel Thompson
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