Commit 7b56fbd8 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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
parents 4312e0e8 cb05143b

arch/x86/kernel/traps.c

+30 −13
Original line number Diff line number Diff line
@@ -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.
@@ -935,6 +936,22 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, 
	irqentry_enter_from_user_mode(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.

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