4.4-stable review patch. If anyone has any objections, please let me know.
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From: Andy Lutomirski luto@kernel.org
commit d8ba61ba58c88d5207c1ba2f7d9a2280e7d03be9 upstream.
There's nothing IST-worthy about #BP/int3. We don't allow kprobes in the small handful of places in the kernel that run at CPL0 with an invalid stack, and 32-bit kernels have used normal interrupt gates for #BP forever.
Furthermore, we don't allow kprobes in places that have usergs while in kernel mode, so "paranoid" is also unnecessary.
Signed-off-by: Andy Lutomirski luto@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/entry/entry_64.S | 2 +- arch/x86/kernel/traps.c | 24 +++++++++++------------- 2 files changed, 12 insertions(+), 14 deletions(-)
--- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1018,7 +1018,7 @@ apicinterrupt3 HYPERVISOR_CALLBACK_VECTO #endif /* CONFIG_HYPERV */
idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK -idtentry int3 do_int3 has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK +idtentry int3 do_int3 has_error_code=0 idtentry stack_segment do_stack_segment has_error_code=1
#ifdef CONFIG_XEN --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -480,7 +480,6 @@ do_general_protection(struct pt_regs *re } NOKPROBE_SYMBOL(do_general_protection);
-/* May run on IST stack. */ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) { #ifdef CONFIG_DYNAMIC_FTRACE @@ -495,7 +494,15 @@ dotraplinkage void notrace do_int3(struc if (poke_int3_handler(regs)) return;
+ /* + * Use ist_enter despite the fact that we don't use an IST stack. + * We can be called from a kprobe in non-CONTEXT_KERNEL kernel + * mode or even during context tracking state changes. + * + * This means that we can't schedule. That's okay. + */ ist_enter(regs); + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, @@ -512,15 +519,9 @@ dotraplinkage void notrace do_int3(struc SIGTRAP) == NOTIFY_STOP) goto exit;
- /* - * Let others (NMI) know that the debug stack is in use - * as we may switch to the interrupt stack. - */ - debug_stack_usage_inc(); preempt_conditional_sti(regs); do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, NULL); preempt_conditional_cli(regs); - debug_stack_usage_dec(); exit: ist_exit(regs); } @@ -886,19 +887,16 @@ void __init trap_init(void) cpu_init();
/* - * X86_TRAP_DB and X86_TRAP_BP have been set - * in early_trap_init(). However, ITS works only after - * cpu_init() loads TSS. See comments in early_trap_init(). + * X86_TRAP_DB was installed in early_trap_init(). However, + * IST works only after cpu_init() loads TSS. See comments + * in early_trap_init(). */ set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK); - /* int3 can be called from all */ - set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK);
x86_init.irqs.trap_init();
#ifdef CONFIG_X86_64 memcpy(&debug_idt_table, &idt_table, IDT_ENTRIES * 16); set_nmi_gate(X86_TRAP_DB, &debug); - set_nmi_gate(X86_TRAP_BP, &int3); #endif }