The following commit has been merged into the x86/entry branch of tip: Commit-ID: d53d9bc0cf783e93b374de3895145c7375e570ba Gitweb: https://git.kernel.org/tip/d53d9bc0cf783e93b374de3895145c7375e570ba Author: Peter Zijlstra <[email protected]> AuthorDate: Wed, 02 Sep 2020 15:26:02 +02:00 Committer: Thomas Gleixner <[email protected]> CommitterDate: Fri, 04 Sep 2020 15:12:58 +02:00
x86/debug: Change thread.debugreg6 to thread.virtual_dr6 Current usage of thread.debugreg6 is convoluted at best. It starts life as a copy of the hardware DR6 value, but then various bits are cleared and set. Replace this with a new variable thread.virtual_dr6 that is initialized to 0 when DR6 is read and only gains bits, at the same time the actual (on stack) dr6 value which is read from the hardware only gets bits cleared. Suggested-by: Andy Lutomirski <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Tested-by: Daniel Thompson <[email protected]> Link: https://lore.kernel.org/r/[email protected] --- arch/x86/include/asm/processor.h | 2 +- arch/x86/kernel/hw_breakpoint.c | 12 +++--------- arch/x86/kernel/kgdb.c | 5 +++-- arch/x86/kernel/ptrace.c | 6 +++--- arch/x86/kernel/traps.c | 25 ++++++++++++++++--------- 5 files changed, 26 insertions(+), 24 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 97143d8..d8a82e6 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -517,7 +517,7 @@ struct thread_struct { /* Save middle states of ptrace breakpoints */ struct perf_event *ptrace_bps[HBP_NUM]; /* Debug status used for traps, single steps, etc... */ - unsigned long debugreg6; + unsigned long virtual_dr6; /* Keep track of the exact dr7 value set by the user */ unsigned long ptrace_dr7; /* Fault info: */ diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index d17a1da..03aa33b 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -454,7 +454,7 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk) t->ptrace_bps[i] = NULL; } - t->debugreg6 = 0; + t->virtual_dr6 = 0; t->ptrace_dr7 = 0; } @@ -489,8 +489,8 @@ static int hw_breakpoint_handler(struct die_args *args) { int i, rc = NOTIFY_STOP; struct perf_event *bp; - unsigned long dr6; unsigned long *dr6_p; + unsigned long dr6; /* The DR6 value is pointed by args->err */ dr6_p = (unsigned long *)ERR_PTR(args->err); @@ -504,12 +504,6 @@ static int hw_breakpoint_handler(struct die_args *args) if ((dr6 & DR_TRAP_BITS) == 0) return NOTIFY_DONE; - /* - * Reset the DRn bits in the virtualized register value. - * The ptrace trigger routine will add in whatever is needed. - */ - current->thread.debugreg6 &= ~DR_TRAP_BITS; - /* Handle all the breakpoints that were triggered */ for (i = 0; i < HBP_NUM; ++i) { if (likely(!(dr6 & (DR_TRAP0 << i)))) @@ -554,7 +548,7 @@ static int hw_breakpoint_handler(struct die_args *args) * breakpoints (to generate signals) and b) when the system has * taken exception due to multiple causes */ - if ((current->thread.debugreg6 & DR_TRAP_BITS) || + if ((current->thread.virtual_dr6 & DR_TRAP_BITS) || (dr6 & (~DR_TRAP_BITS))) rc = NOTIFY_DONE; diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c index c2f02f3..ff7878d 100644 --- a/arch/x86/kernel/kgdb.c +++ b/arch/x86/kernel/kgdb.c @@ -629,9 +629,10 @@ static void kgdb_hw_overflow_handler(struct perf_event *event, struct task_struct *tsk = current; int i; - for (i = 0; i < 4; i++) + for (i = 0; i < 4; i++) { if (breakinfo[i].enabled) - tsk->thread.debugreg6 |= (DR_TRAP0 << i); + tsk->thread.virtual_dr6 |= (DR_TRAP0 << i); + } } void kgdb_arch_late(void) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 5f98289..bedca01 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -465,7 +465,7 @@ static void ptrace_triggered(struct perf_event *bp, break; } - thread->debugreg6 |= (DR_TRAP0 << i); + thread->virtual_dr6 |= (DR_TRAP0 << i); } /* @@ -601,7 +601,7 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n) if (bp) val = bp->hw.info.address; } else if (n == 6) { - val = thread->debugreg6 ^ DR6_RESERVED; /* Flip back to arch polarity */ + val = thread->virtual_dr6 ^ DR6_RESERVED; /* Flip back to arch polarity */ } else if (n == 7) { val = thread->ptrace_dr7; } @@ -657,7 +657,7 @@ static int ptrace_set_debugreg(struct task_struct *tsk, int n, if (n < HBP_NUM) { rc = ptrace_set_breakpoint_addr(tsk, n, val); } else if (n == 6) { - thread->debugreg6 = val ^ DR6_RESERVED; /* Flip to positive polarity */ + thread->virtual_dr6 = val ^ DR6_RESERVED; /* Flip to positive polarity */ rc = 0; } else if (n == 7) { rc = ptrace_write_dr7(tsk, val); diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 114515b..df9c655 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -749,6 +749,12 @@ static __always_inline unsigned long debug_read_clear_dr6(void) 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. @@ -785,17 +791,16 @@ static __always_inline unsigned long debug_read_clear_dr6(void) static bool notify_debug(struct pt_regs *regs, unsigned long *dr6) { - struct task_struct *tsk = current; - - /* Store the virtualized DR6 value */ - tsk->thread.debugreg6 = *dr6; - + /* + * Notifiers will clear bits in @dr6 to indicate the event has been + * consumed - hw_breakpoint_handler(), single_stop_cont(). + * + * Notifiers will set bits in @virtual_dr6 to indicate the desire + * for signals - ptrace_triggered(), kgdb_hw_overflow_handler(). + */ if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP) return true; - /* Reload the DR6 value, the notifier might have changed it */ - *dr6 = tsk->thread.debugreg6; - return false; } @@ -853,7 +858,7 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, * 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)) + if (WARN_ON_ONCE(dr6 & DR_STEP)) regs->flags &= ~X86_EFLAGS_TF; out: instrumentation_end(); @@ -903,6 +908,8 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, goto out_irq; } + /* Add the virtual_dr6 bits for signals. */ + dr6 |= current->thread.virtual_dr6; if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp) send_sigtrap(regs, 0, get_si_code(dr6));
