From 9347f41352181bf4a7e663f7b5f4a4bb32244d73 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 4 May 2020 19:56:26 +0200 Subject: [PATCH] x86/traps: Restructure #DB handling Now that there are separate entry points, move the kernel/user_mode specifc checks into the entry functions so the common handling code does not need the extra mode checks. Make the code more readable while at it. Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Acked-by: Andy Lutomirski Link: https://lkml.kernel.org/r/20200505135315.283276272@linutronix.de --- arch/x86/kernel/traps.c | 69 +++++++++++++++++++++++++------------------------ 1 file changed, 35 insertions(+), 34 deletions(-) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 4f248c5..b62e962 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -775,39 +775,12 @@ static __always_inline void debug_exit(unsigned long dr7) * * May run on IST stack. */ -static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6) +static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6, + bool user_icebp) { struct task_struct *tsk = current; - int user_icebp = 0; int si_code; - /* - * 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_tsk_thread_flag(tsk, TIF_BLOCKSTEP); - - if (unlikely(!user_mode(regs) && (dr6 & DR_STEP) && - is_sysenter_singlestep(regs))) { - dr6 &= ~DR_STEP; - if (!dr6) - return; - /* - * else we might have gotten a single-step trap and hit a - * watchpoint at the same time, in which case we should fall - * through and handle the watchpoint. - */ - } - - /* - * 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. - */ - if (!dr6 && user_mode(regs)) - user_icebp = 1; - /* Store the virtualized DR6 value */ tsk->thread.debugreg6 = dr6; @@ -832,9 +805,7 @@ static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6) if (v8086_mode(regs)) { handle_vm86_trap((struct kernel_vm86_regs *) regs, 0, X86_TRAP_DB); - cond_local_irq_disable(regs); - debug_stack_usage_dec(); - return; + goto out; } if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) { @@ -848,9 +819,12 @@ static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6) set_tsk_thread_flag(tsk, TIF_SINGLESTEP); regs->flags &= ~X86_EFLAGS_TF; } + si_code = get_si_code(tsk->thread.debugreg6); if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp) send_sigtrap(regs, 0, si_code); + +out: cond_local_irq_disable(regs); debug_stack_usage_dec(); } @@ -859,7 +833,27 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, unsigned long dr6) { nmi_enter(); - handle_debug(regs, dr6); + /* + * 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); + + /* + * Catch SYSENTER with TF set and clear DR_STEP. If this hit a + * watchpoint at the same time then that will still be handled. + */ + if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs)) + dr6 &= ~DR_STEP; + + /* + * If DR6 is zero, no point in trying to handle it. The kernel is + * not using INT1. + */ + if (dr6) + handle_debug(regs, dr6, false); + nmi_exit(); } @@ -867,7 +861,14 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, unsigned long dr6) { idtentry_enter(regs); - handle_debug(regs, dr6); + 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. + */ + handle_debug(regs, dr6, !dr6); idtentry_exit(regs); } -- 2.7.4