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 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From d8ba61ba58c88d5207c1ba2f7d9a2280e7d03be9 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski luto@kernel.org 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@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/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 @@ -1097,7 +1097,7 @@ 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 @@ -577,7 +577,6 @@ 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 @@ -592,6 +591,13 @@ 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 @@ -609,15 +615,10 @@ 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@kernel.org are
queue-4.15/x86-entry-64-don-t-use-ist-entry-for-bp-stack.patch queue-4.15/selftests-x86-ptrace_syscall-fix-for-yet-more-glibc-interference.patch queue-4.15/x86-vsyscall-64-use-proper-accessor-to-update-p4d-entry.patch queue-4.15/kvm-x86-fix-icebp-instruction-handling.patch