From: "tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Kyle Huey <me@kylehuey.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>, x86 <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/urgent] x86/debug: Fix DR_STEP vs ptrace_get_debugreg(6)
Date: Tue, 27 Oct 2020 22:19:09 -0000 [thread overview]
Message-ID: <160383714941.397.12811023630821434314.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20201027183330.GM2628@hirez.programming.kicks-ass.net>
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: cb05143bdf428f280a5d519c82abf196d7871c11
Gitweb: https://git.kernel.org/tip/cb05143bdf428f280a5d519c82abf196d7871c11
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 27 Oct 2020 19:33:30 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 27 Oct 2020 23:15:24 +01:00
x86/debug: Fix DR_STEP vs ptrace_get_debugreg(6)
Commit d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to
thread.virtual_dr6") changed the semantics of the variable from random
collection of bits, to exactly only those bits that ptrace() needs.
Unfortunately this lost DR_STEP for PTRACE_{BLOCK,SINGLE}STEP.
Furthermore, it turns out that userspace expects DR_STEP to be
unconditionally available, even for manual TF usage outside of
PTRACE_{BLOCK,SINGLE}_STEP.
Fixes: d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to thread.virtual_dr6")
Reported-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kyle Huey <me@kylehuey.com>
Link: https://lore.kernel.org/r/20201027183330.GM2628@hirez.programming.kicks-ass.net
---
arch/x86/kernel/traps.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 32b2d39..e19df6c 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -937,10 +937,13 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
instrumentation_begin();
/*
- * Clear the virtual DR6 value, ptrace() routines will set bits here
- * for things it wants signals for.
+ * Start the virtual/ptrace DR6 value with just the DR_STEP mask
+ * of the real DR6. ptrace_triggered() will set the DR_TRAPn bits.
+ *
+ * Userspace expects DR_STEP to be visible in ptrace_get_debugreg(6)
+ * even if it is not the result of PTRACE_SINGLESTEP.
*/
- current->thread.virtual_dr6 = 0;
+ current->thread.virtual_dr6 = (dr6 & DR_STEP);
/*
* The SDM says "The processor clears the BTF flag when it
prev parent reply other threads:[~2020-10-27 22:19 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-27 9:15 [PATCH 0/3] x86/debug: Fixes Peter Zijlstra
2020-10-27 9:15 ` [PATCH 1/3] x86/debug: Fix BTF handling Peter Zijlstra
2020-10-27 19:41 ` Peter Zijlstra
2020-10-28 9:20 ` Masami Hiramatsu
2020-10-28 9:59 ` Peter Zijlstra
2020-10-28 12:11 ` Masami Hiramatsu
2020-10-28 14:31 ` [PATCH] x86/kprobes: Restore BTF if the single-stepping is cancelled Masami Hiramatsu
2020-12-07 23:22 ` Steven Rostedt
2020-12-09 18:44 ` [tip: perf/core] " tip-bot2 for Masami Hiramatsu
2020-10-27 22:19 ` [tip: x86/urgent] x86/debug: Fix BTF handling tip-bot2 for Peter Zijlstra
2020-10-27 9:15 ` [PATCH 2/3] x86/debug: Only clear/set ->virtual_dr6 for userspace #DB Peter Zijlstra
2020-10-27 22:19 ` [tip: x86/urgent] " tip-bot2 for Peter Zijlstra
2020-10-27 9:15 ` [PATCH 3/3] x86/debug: Fix PTRACE_{BLOCK,SINGLE}STEP vs ptrace_get_debugreg(6) Peter Zijlstra
2020-10-27 17:22 ` Kyle Huey
2020-10-27 18:33 ` [PATCH v2 3/3] Fix DR_STEP " Peter Zijlstra
2020-10-27 22:19 ` tip-bot2 for Peter Zijlstra [this message]
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