This is a note to let you know that I've just added the patch titled
x86/entry/64: Don't use IST entry for #BP stack
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-entry-64-don-t-use-ist-entry-for-bp-stack.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From d8ba61ba58c88d5207c1ba2f7d9a2280e7d03be9 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Thu, 23 Jul 2015 15:37:48 -0700
Subject: x86/entry/64: Don't use IST entry for #BP stack
From: Andy Lutomirski <luto@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
}
Patches currently in stable-queue which might be from luto@xxxxxxxxxx are
queue-4.4/x86-entry-64-don-t-use-ist-entry-for-bp-stack.patch
queue-4.4/kvm-x86-fix-icebp-instruction-handling.patch