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x86/entry: Re-order #DB handler to avoid *SAN instrumentation

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vmlinux.o: warning: objtool: exc_debug()+0xbb: call to clear_ti_thread_flag.constprop.0() leaves .noinstr.text section
vmlinux.o: warning: objtool: noist_exc_debug()+0x55: call to clear_ti_thread_flag.constprop.0() leaves .noinstr.text section

Rework things so that handle_debug() looses the noinstr and move the
clear_thread_flag() into that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200603114052.127756554@infradead.org
This commit is contained in:
Peter Zijlstra
2020-06-03 13:40:20 +02:00
committed by Thomas Gleixner
parent 4b281e541b
commit 5ef2279331
1 changed files with 27 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

55
arch/x86/kernel/traps.c
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@@ -775,26 +775,44 @@ static __always_inline void debug_exit(unsigned long dr7)
* *
* May run on IST stack. * May run on IST stack.
*/ */
static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6, static void handle_debug(struct pt_regs *regs, unsigned long dr6, bool user)
bool user_icebp)
{ {
struct task_struct *tsk = current; struct task_struct *tsk = current;
bool user_icebp;
int si_code; 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_thread_flag(TIF_BLOCKSTEP);
/*
* If DR6 is zero, no point in trying to handle it. The kernel is
* not using INT1.
*/
if (!user && !dr6)
return;
/*
* 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.
*/
user_icebp = user && !dr6;
/* Store the virtualized DR6 value */ /* Store the virtualized DR6 value */
tsk->thread.debugreg6 = dr6; tsk->thread.debugreg6 = dr6;
instrumentation_begin();
#ifdef CONFIG_KPROBES #ifdef CONFIG_KPROBES
if (kprobe_debug_handler(regs)) { if (kprobe_debug_handler(regs)) {
instrumentation_end();
return; return;
} }
#endif #endif
if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0, if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,
SIGTRAP) == NOTIFY_STOP) { SIGTRAP) == NOTIFY_STOP) {
instrumentation_end();
return; return;
} }
@@ -825,7 +843,6 @@ static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,
out: out:
cond_local_irq_disable(regs); cond_local_irq_disable(regs);
instrumentation_end();
} }
static __always_inline void exc_debug_kernel(struct pt_regs *regs, static __always_inline void exc_debug_kernel(struct pt_regs *regs,
@@ -834,14 +851,6 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
nmi_enter(); nmi_enter();
instrumentation_begin(); instrumentation_begin();
trace_hardirqs_off_finish(); trace_hardirqs_off_finish();
instrumentation_end();
/*
* 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 * Catch SYSENTER with TF set and clear DR_STEP. If this hit a
@@ -850,14 +859,8 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs)) if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))
dr6 &= ~DR_STEP; dr6 &= ~DR_STEP;
/* handle_debug(regs, dr6, false);
* If DR6 is zero, no point in trying to handle it. The kernel is
* not using INT1.
*/
if (dr6)
handle_debug(regs, dr6, false);
instrumentation_begin();
if (regs->flags & X86_EFLAGS_IF) if (regs->flags & X86_EFLAGS_IF)
trace_hardirqs_on_prepare(); trace_hardirqs_on_prepare();
instrumentation_end(); instrumentation_end();
@@ -868,14 +871,10 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
unsigned long dr6) unsigned long dr6)
{ {
idtentry_enter_user(regs); idtentry_enter_user(regs);
clear_thread_flag(TIF_BLOCKSTEP); instrumentation_begin();
/* handle_debug(regs, dr6, true);
* If dr6 has no reason to give us about the origin of this trap, instrumentation_end();
* 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_user(regs); idtentry_exit_user(regs);
} }