| 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
| ||
|
Date: Wed, 10 Jan 2018 19:54:24 -0500
From: Brian Gerst <brgerst@...il.com>
To: Andi Kleen <andi@...stfloor.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
"the arch/x86 maintainers" <x86@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
David Woodhouse <dwmw@...zon.co.uk>,
Paul Turner <pjt@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Tom Lendacky <thomas.lendacky@....com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
Dave Hansen <dave.hansen@...el.com>,
Jiri Kosina <jikos@...nel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1 1/8] x86/entry/clearregs: Remove partial stack frame in
fast system call
On Wed, Jan 10, 2018 at 7:16 PM, Andi Kleen <andi@...stfloor.org> wrote:
> On Tue, Jan 09, 2018 at 09:46:16PM -0500, Brian Gerst wrote:
>> On Tue, Jan 9, 2018 at 8:03 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> > From: Andi Kleen <ak@...ux.intel.com>
>> >
>> > Remove the partial stack frame in the 64bit syscall fast path.
>> > In the next patch we want to clear the extra registers, which requires
>> > to always save all registers. So remove the partial stack frame
>> > in the syscall fast path and always save everything.
>> >
>> > This actually simplifies the code because the ptregs stubs
>> > are not needed anymore.
>> >
>> > arch/x86/entry/entry_64.S | 57 ++++-----------------------------------------------------
>> > arch/x86/entry/syscall_64.c | 2 +-
>> >
>> > Signed-off-by: Andi Kleen <ak@...ux.intel.com>
>> > ---
>> > arch/x86/entry/entry_64.S | 57 ++++-----------------------------------------
>> > arch/x86/entry/syscall_64.c | 2 +-
>> > 2 files changed, 5 insertions(+), 54 deletions(-)
>> >
>> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> > index 58dbf7a12a05..bbdfbdd817d6 100644
>> > --- a/arch/x86/entry/entry_64.S
>> > +++ b/arch/x86/entry/entry_64.S
>> > @@ -234,7 +234,9 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)
>> > pushq %r9 /* pt_regs->r9 */
>> > pushq %r10 /* pt_regs->r10 */
>> > pushq %r11 /* pt_regs->r11 */
>> > - sub $(6*8), %rsp /* pt_regs->bp, bx, r12-15 not saved */
>> > + sub $(6*8), %rsp
>> > + SAVE_EXTRA_REGS
>> > +
>>
>> Continue using pushes here
>>
>> > UNWIND_HINT_REGS extra=0
>> >
>> > /*
>> > @@ -262,11 +264,6 @@ entry_SYSCALL_64_fastpath:
>> > ja 1f /* return -ENOSYS (already in pt_regs->ax) */
>> > movq %r10, %rcx
>> >
>> > - /*
>> > - * This call instruction is handled specially in stub_ptregs_64.
>> > - * It might end up jumping to the slow path. If it jumps, RAX
>> > - * and all argument registers are clobbered.
>> > - */
>> > #ifdef CONFIG_RETPOLINE
>> > movq sys_call_table(, %rax, 8), %rax
>> > call __x86_indirect_thunk_rax
>> > @@ -293,9 +290,7 @@ entry_SYSCALL_64_fastpath:
>> > TRACE_IRQS_ON /* user mode is traced as IRQs on */
>> > movq RIP(%rsp), %rcx
>> > movq EFLAGS(%rsp), %r11
>> > - addq $6*8, %rsp /* skip extra regs -- they were preserved */
>> > - UNWIND_HINT_EMPTY
>> > - jmp .Lpop_c_regs_except_rcx_r11_and_sysret
>> > + jmp syscall_return_via_sysret
>> >
>> > 1:
>> > /*
>> > @@ -305,14 +300,12 @@ entry_SYSCALL_64_fastpath:
>> > */
>> > TRACE_IRQS_ON
>> > ENABLE_INTERRUPTS(CLBR_ANY)
>> > - SAVE_EXTRA_REGS
>> > movq %rsp, %rdi
>> > call syscall_return_slowpath /* returns with IRQs disabled */
>> > jmp return_from_SYSCALL_64
>> >
>> > entry_SYSCALL64_slow_path:
>> > /* IRQs are off. */
>> > - SAVE_EXTRA_REGS
>> > movq %rsp, %rdi
>> > call do_syscall_64 /* returns with IRQs disabled */
>> >
>> > @@ -389,7 +382,6 @@ syscall_return_via_sysret:
>> > /* rcx and r11 are already restored (see code above) */
>> > UNWIND_HINT_EMPTY
>> > POP_EXTRA_REGS
>> > -.Lpop_c_regs_except_rcx_r11_and_sysret:
>> > popq %rsi /* skip r11 */
>> > popq %r10
>> > popq %r9
>> > @@ -420,47 +412,6 @@ syscall_return_via_sysret:
>> > USERGS_SYSRET64
>> > END(entry_SYSCALL_64)
>> >
>> > -ENTRY(stub_ptregs_64)
>> > - /*
>> > - * Syscalls marked as needing ptregs land here.
>> > - * If we are on the fast path, we need to save the extra regs,
>> > - * which we achieve by trying again on the slow path. If we are on
>> > - * the slow path, the extra regs are already saved.
>> > - *
>> > - * RAX stores a pointer to the C function implementing the syscall.
>> > - * IRQs are on.
>> > - */
>> > - cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp)
>> > - jne 1f
>> > -
>> > - /*
>> > - * Called from fast path -- disable IRQs again, pop return address
>> > - * and jump to slow path
>> > - */
>> > - DISABLE_INTERRUPTS(CLBR_ANY)
>> > - TRACE_IRQS_OFF
>> > - popq %rax
>> > - UNWIND_HINT_REGS extra=0
>> > - jmp entry_SYSCALL64_slow_path
>> > -
>> > -1:
>> > - JMP_NOSPEC %rax /* Called from C */
>> > -END(stub_ptregs_64)
>> > -
>> > -.macro ptregs_stub func
>> > -ENTRY(ptregs_\func)
>> > - UNWIND_HINT_FUNC
>> > - leaq \func(%rip), %rax
>> > - jmp stub_ptregs_64
>> > -END(ptregs_\func)
>> > -.endm
>> > -
>> > -/* Instantiate ptregs_stub for each ptregs-using syscall */
>> > -#define __SYSCALL_64_QUAL_(sym)
>> > -#define __SYSCALL_64_QUAL_ptregs(sym) ptregs_stub sym
>> > -#define __SYSCALL_64(nr, sym, qual) __SYSCALL_64_QUAL_##qual(sym)
>> > -#include <asm/syscalls_64.h>
>> > -
>>
>> You can't just blindly remove this. We need to make sure that
>> syscalls that modify registers take the slow path exit, because they
>> may change the registers to be incompatible with SYSRET.
>
> That's a good point. I checked the ptregs calls:
>
> iopl: should be fine, we will be restoring the correct IOPL through
> SYSRET
> clone/fork: fine too, the original return is fine and ret_from_fork
> takes care of the child
> execve et.al.: we will be leaking r11(rflags), rcx(orig return) into
> the new process. but that seems acceptable.
We still need to check if we are loading a 32-bit binary. That must
return with IRET.
> rt_sigreturn: that's the only one who has problems. I added a new
> TIF_FULL_RESTORE to force it into the slow path.
--
Brian Gerst
Powered by blists - more mailing lists