| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAMzpN2g4zmCyo183-n7KKAoeMa-ctmcn5YequZOGEYDydQ+EpQ@mail.gmail.com>
Date: Wed, 14 Feb 2018 14:27:17 -0500
From: Brian Gerst <brgerst@...il.com>
To: Dominik Brodowski <linux@...inikbrodowski.net>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
"the arch/x86 maintainers" <x86@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Andi Kleen <ak@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
"Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [RFC PATCH 3/4] x86/entry/64: move switch_to_thread_stack to
interrupt helper function
On Wed, Feb 14, 2018 at 2:06 PM, Dominik Brodowski
<linux@...inikbrodowski.net> wrote:
> On Wed, Feb 14, 2018 at 01:57:15PM -0500, Brian Gerst wrote:
>> On Wed, Feb 14, 2018 at 1:21 PM, Dominik Brodowski
>> <linux@...inikbrodowski.net> wrote:
>> > We can also move the SWAPGS and the switch_to_thread_stack to the
>> > interrupt helper function. As we do not want call depths of two,
>> > convert switch_to_thread_stack to a macro. However, as entry_64_compat.S
>> > expects switch_to_thread_stack to be a function, provide a wrapper for
>> > that, which leads to some code duplication if CONFIG_IA32_EMULATION is
>> > enabled. Therefore, the size reduction differs slightly:
>> >
>> > With CONFIG_IA32_EMULATION enabled (-0.13k):
>> > text data bss dec hex filename
>> > 16897 0 0 16897 4201 entry_64.o-orig
>> > 16767 0 0 16767 417f entry_64.o
>> >
>> > With CONFIG_IA32_EMULATION disabled (-0.27k):
>> > text data bss dec hex filename
>> > 16897 0 0 16897 4201 entry_64.o-orig
>> > 16622 0 0 16622 40ee entry_64.o
>> >
>> > Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
>> > ---
>> > arch/x86/entry/entry_64.S | 65 ++++++++++++++++++++++++++---------------------
>> > 1 file changed, 36 insertions(+), 29 deletions(-)
>> >
>> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> > index 3046b12a1acb..b60a3b692ca9 100644
>> > --- a/arch/x86/entry/entry_64.S
>> > +++ b/arch/x86/entry/entry_64.S
>> > @@ -536,6 +536,31 @@ END(irq_entries_start)
>> > decl PER_CPU_VAR(irq_count)
>> > .endm
>> >
>> > +/*
>> > + * Switch to the thread stack. This is called with the IRET frame and
>> > + * orig_ax on the stack. (That is, RDI..R12 are not on the stack and
>> > + * space has not been allocated for them.)
>> > + */
>> > +.macro DO_SWITCH_TO_THREAD_STACK
>> > + pushq %rdi
>> > + /* Need to switch before accessing the thread stack. */
>> > + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
>> > + movq %rsp, %rdi
>> > + movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
>> > + UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI
>> > +
>> > + pushq 7*8(%rdi) /* regs->ss */
>> > + pushq 6*8(%rdi) /* regs->rsp */
>> > + pushq 5*8(%rdi) /* regs->eflags */
>> > + pushq 4*8(%rdi) /* regs->cs */
>> > + pushq 3*8(%rdi) /* regs->ip */
>> > + pushq 2*8(%rdi) /* regs->orig_ax */
>> > + pushq 8(%rdi) /* return address */
>> > + UNWIND_HINT_FUNC
>> > +
>> > + movq (%rdi), %rdi
>> > +.endm
>> > +
>> > /*
>> > * Interrupt entry/exit.
>> > *
>> > @@ -543,10 +568,17 @@ END(irq_entries_start)
>> > *
>> > * Entry runs with interrupts off.
>> > */
>> > +/* 8(%rsp): ~(interrupt number) */
>> > ENTRY(interrupt_helper)
>> > UNWIND_HINT_FUNC
>> > cld
>> >
>> > + testb $3, CS-ORIG_RAX+8(%rsp)
>> > + jz 1f
>> > + SWAPGS
>> > + DO_SWITCH_TO_THREAD_STACK
>> > +1:
>> > +
>> > PUSH_AND_CLEAR_REGS save_ret=1
>> > ENCODE_FRAME_POINTER 8
>> >
>> > @@ -579,12 +611,6 @@ END(interrupt_helper)
>> > .macro interrupt func
>> > cld
>> >
>> > - testb $3, CS-ORIG_RAX(%rsp)
>> > - jz 1f
>> > - SWAPGS
>> > - call switch_to_thread_stack
>> > -1:
>> > -
>> > call interrupt_helper
>> >
>> > call \func /* rdi points to pt_regs */
>> > @@ -853,33 +879,14 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
>> > */
>> > #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8)
>> >
>> > -/*
>> > - * Switch to the thread stack. This is called with the IRET frame and
>> > - * orig_ax on the stack. (That is, RDI..R12 are not on the stack and
>> > - * space has not been allocated for them.)
>> > - */
>> > +#if defined(CONFIG_IA32_EMULATION)
>> > +/* entry_64_compat.S::entry_INT80_compat expects this to be an ASM function */
>> > ENTRY(switch_to_thread_stack)
>> > UNWIND_HINT_FUNC
>> > -
>> > - pushq %rdi
>> > - /* Need to switch before accessing the thread stack. */
>> > - SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
>> > - movq %rsp, %rdi
>> > - movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
>> > - UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI
>> > -
>> > - pushq 7*8(%rdi) /* regs->ss */
>> > - pushq 6*8(%rdi) /* regs->rsp */
>> > - pushq 5*8(%rdi) /* regs->eflags */
>> > - pushq 4*8(%rdi) /* regs->cs */
>> > - pushq 3*8(%rdi) /* regs->ip */
>> > - pushq 2*8(%rdi) /* regs->orig_ax */
>> > - pushq 8(%rdi) /* return address */
>> > - UNWIND_HINT_FUNC
>> > -
>> > - movq (%rdi), %rdi
>> > + DO_SWITCH_TO_THREAD_STACK
>> > ret
>> > END(switch_to_thread_stack)
>> > +#endif
>> >
>> > .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
>> > ENTRY(\sym)
>> > --
>> > 2.16.1
>> >
>>
>> Move the macro to calling.h, and inline it into the compat entry.
>
> That certainly sounds possible, but makes the macro more complex: Inlining
> means that the offsets need to be reduced by -8. But we need the current
> offset for the call from interrupt_helper. So such a change might make the
> code less readable.
>
> Thanks,
> Dominik
It would probably be better to just open code it then, without the
return address handling.
--
Brian Gerst
Powered by blists - more mailing lists