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 4.14-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-4.14 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/idt.c | 2 --
arch/x86/kernel/traps.c | 15 ++++++++-------
3 files changed, 9 insertions(+), 10 deletions(-)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1091,7 +1091,7 @@ 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/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -160,7 +160,6 @@ static const __initconst struct idt_data
*/
static const __initconst struct idt_data dbg_idts[] = {
INTG(X86_TRAP_DB, debug),
- INTG(X86_TRAP_BP, int3),
};
#endif
@@ -183,7 +182,6 @@ gate_desc debug_idt_table[IDT_ENTRIES] _
static const __initconst struct idt_data ist_idts[] = {
ISTG(X86_TRAP_DB, debug, DEBUG_STACK),
ISTG(X86_TRAP_NMI, nmi, NMI_STACK),
- SISTG(X86_TRAP_BP, int3, DEBUG_STACK),
ISTG(X86_TRAP_DF, double_fault, DOUBLEFAULT_STACK),
#ifdef CONFIG_X86_MCE
ISTG(X86_TRAP_MC, &machine_check, MCE_STACK),
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -571,7 +571,6 @@ 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
@@ -586,6 +585,13 @@ 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
@@ -603,15 +609,10 @@ 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();
cond_local_irq_enable(regs);
do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, NULL);
cond_local_irq_disable(regs);
- debug_stack_usage_dec();
+
exit:
ist_exit(regs);
}
Patches currently in stable-queue which might be from luto@xxxxxxxxxx are
queue-4.14/x86-entry-64-don-t-use-ist-entry-for-bp-stack.patch
queue-4.14/selftests-x86-ptrace_syscall-fix-for-yet-more-glibc-interference.patch
queue-4.14/x86-vsyscall-64-use-proper-accessor-to-update-p4d-entry.patch
queue-4.14/kvm-x86-fix-icebp-instruction-handling.patch