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authorLinus Torvalds <torvalds@linux-foundation.org>2020-11-01 11:21:26 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-11-01 11:21:26 -0800
commit7b56fbd83e261484da43f04090bce07570bd117f (patch)
treed8b5e4182098d607c8a15119c55d33d50bc1bc4b /arch
parent4312e0e8d3eab027d9506db091eb10e6a9ff25d3 (diff)
parentcb05143bdf428f280a5d519c82abf196d7871c11 (diff)
Merge tag 'x86-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fixes from Thomas Gleixner: "Three fixes all related to #DB: - Handle the BTF bit correctly so it doesn't get lost due to a kernel #DB - Only clear and set the virtual DR6 value used by ptrace on user space triggered #DB. A kernel #DB must leave it alone to ensure data consistency for ptrace. - Make the bitmasking of the virtual DR6 storage correct so it does not lose DR_STEP" * tag 'x86-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/debug: Fix DR_STEP vs ptrace_get_debugreg(6) x86/debug: Only clear/set ->virtual_dr6 for userspace #DB x86/debug: Fix BTF handling
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/traps.c43
1 files changed, 30 insertions, 13 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3c70fb34028b..e19df6cde35d 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -793,19 +793,6 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
set_debugreg(DR6_RESERVED, 6);
dr6 ^= DR6_RESERVED; /* Flip to positive polarity */
- /*
- * Clear the virtual DR6 value, ptrace routines will set bits here for
- * things we want signals for.
- */
- current->thread.virtual_dr6 = 0;
-
- /*
- * The SDM says "The processor clears the BTF flag when it
- * generates a debug exception." Clear TIF_BLOCKSTEP to keep
- * TIF_BLOCKSTEP in sync with the hardware BTF flag.
- */
- clear_thread_flag(TIF_BLOCKSTEP);
-
return dr6;
}
@@ -873,6 +860,20 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
*/
WARN_ON_ONCE(user_mode(regs));
+ if (test_thread_flag(TIF_BLOCKSTEP)) {
+ /*
+ * The SDM says "The processor clears the BTF flag when it
+ * generates a debug exception." but PTRACE_BLOCKSTEP requested
+ * it for userspace, but we just took a kernel #DB, so re-set
+ * BTF.
+ */
+ unsigned long debugctl;
+
+ rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+ debugctl |= DEBUGCTLMSR_BTF;
+ wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+ }
+
/*
* Catch SYSENTER with TF set and clear DR_STEP. If this hit a
* watchpoint at the same time then that will still be handled.
@@ -936,6 +937,22 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
instrumentation_begin();
/*
+ * 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 = (dr6 & DR_STEP);
+
+ /*
+ * The SDM says "The processor clears the BTF flag when it
+ * generates a debug exception." Clear TIF_BLOCKSTEP to keep
+ * TIF_BLOCKSTEP in sync with the hardware BTF flag.
+ */
+ clear_thread_flag(TIF_BLOCKSTEP);
+
+ /*
* If dr6 has no reason to give us about the origin of this trap,
* then it's very likely the result of an icebp/int01 trap.
* User wants a sigtrap for that.

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