From: Dave Hansen <dave.hansen@linux.intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
moritz.lipp@iaik.tugraz.at,
Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
michael.schwarz@iaik.tugraz.at,
richard.fellner@student.tugraz.at,
Linus Torvalds <torvalds@linux-foundation.org>,
Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>,
X86 ML <x86@kernel.org>
Subject: Re: [PATCH 11/23] x86, kaiser: map entry stack variables
Date: Thu, 23 Nov 2017 07:37:33 -0800 [thread overview]
Message-ID: <ecccf06a-5791-f105-c080-01af351c0bc4@linux.intel.com> (raw)
In-Reply-To: <CALCETrWM7OytAXOP9Jb1Ss0=75bGB-XSCLounC2z7xauG6CABQ@mail.gmail.com>
On 11/22/2017 07:31 PM, Andy Lutomirski wrote:
> On Wed, Nov 22, 2017 at 4:34 PM, Dave Hansen
> <dave.hansen@linux.intel.com> wrote:
>>
>> From: Dave Hansen <dave.hansen@linux.intel.com>
>>
>> There are times where the kernel is entered but there is not a
>> safe stack, like at SYSCALL entry. To obtain a safe stack, the
>> per-cpu variables 'rsp_scratch' and 'cpu_current_top_of_stack'
>> are used to save the old %rsp value and to find where the kernel
>> stack should start.
>>
>> You can not directly manipulate the CR3 register. You can only
>> 'MOV' to it from another register, which means a register must be
>> clobbered in order to do any CR3 manipulation. User-mapping
>> these variables allows us to obtain a safe stack and use it for
>> temporary storage *before* CR3 is switched.
>>
>> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
>> Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
>> Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
>> Cc: Richard Fellner <richard.fellner@student.tugraz.at>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
>> Cc: Kees Cook <keescook@google.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: x86@kernel.org
>> ---
>>
>> b/arch/x86/kernel/cpu/common.c | 2 +-
>> b/arch/x86/kernel/process_64.c | 2 +-
>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff -puN arch/x86/kernel/cpu/common.c~kaiser-user-map-stack-helper-vars arch/x86/kernel/cpu/common.c
>> --- a/arch/x86/kernel/cpu/common.c~kaiser-user-map-stack-helper-vars 2017-11-22 15:45:50.128619736 -0800
>> +++ b/arch/x86/kernel/cpu/common.c 2017-11-22 15:45:50.134619736 -0800
>> @@ -1524,7 +1524,7 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count);
>> * the top of the kernel stack. Use an extra percpu variable to track the
>> * top of the kernel stack directly.
>> */
>> -DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) =
>> +DEFINE_PER_CPU_USER_MAPPED(unsigned long, cpu_current_top_of_stack) =
>> (unsigned long)&init_thread_union + THREAD_SIZE;
>
> This is in an x86_32-only section and should be dropped, I think.
It's used in entry_SYSCALL_64 (see below). But I do think it's safe to
drop now. We switch before we use it.
>> diff -puN arch/x86/kernel/process_64.c~kaiser-user-map-stack-helper-vars arch/x86/kernel/process_64.c
>> --- a/arch/x86/kernel/process_64.c~kaiser-user-map-stack-helper-vars 2017-11-22 15:45:50.130619736 -0800
>> +++ b/arch/x86/kernel/process_64.c 2017-11-22 15:45:50.134619736 -0800
>> @@ -59,7 +59,7 @@
>> #include <asm/unistd_32_ia32.h>
>> #endif
>>
>> -__visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
>> +__visible DEFINE_PER_CPU_USER_MAPPED(unsigned long, rsp_scratch);
>>
> This shouldn't be needed any more either.
What about this hunk? It touches rsp_scratch before switching:
@@ -207,9 +210,16 @@ ENTRY(entry_SYSCALL_64)
swapgs
movq %rsp, PER_CPU_VAR(rsp_scratch)
- movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
- TRACE_IRQS_OFF
+ /*
+ * The kernel CR3 is needed to map the process stack, but we
+ * need a scratch register to be able to load CR3. %rsp is
+ * clobberable right now, so use it as a scratch register.
+ * %rsp will be look crazy here for a couple instructions.
+ */
+ SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
+
+ movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
next prev parent reply other threads:[~2017-11-23 15:37 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-23 0:34 [PATCH 00/23] [v4] KAISER: unmap most of the kernel from userspace page tables Dave Hansen
2017-11-23 0:34 ` [PATCH 01/23] x86, kaiser: disable global pages by default with KAISER Dave Hansen
2017-11-23 0:34 ` [PATCH 02/23] x86, kaiser: prepare assembly for entry/exit CR3 switching Dave Hansen
2017-11-23 0:34 ` [PATCH 03/23] x86, kaiser: introduce user-mapped per-cpu areas Dave Hansen
2017-11-23 0:34 ` [PATCH 04/23] x86, kaiser: mark per-cpu data structures required for entry/exit Dave Hansen
2017-11-23 0:34 ` [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch) Dave Hansen
2017-11-23 4:07 ` Andy Lutomirski
2017-11-26 16:10 ` Andy Lutomirski
2017-11-26 16:24 ` Dave Hansen
2017-11-26 16:29 ` Andy Lutomirski
2018-01-05 4:16 ` Yisheng Xie
2018-01-05 5:18 ` Dave Hansen
2018-01-05 6:16 ` Yisheng Xie
2018-01-05 6:29 ` Dave Hansen
2018-01-05 11:49 ` Andrea Arcangeli
2018-01-05 18:19 ` Jiri Kosina
2018-01-05 19:00 ` Jiri Kosina
2018-01-05 19:03 ` Dave Hansen
2018-01-05 19:17 ` Jiri Kosina
2018-01-05 19:18 ` Jiri Kosina
2018-01-05 19:55 ` Andrea Arcangeli
2018-01-05 21:07 ` Dave Hansen
2018-01-05 21:14 ` Jiri Kosina
2018-01-05 21:29 ` Andy Lutomirski
2018-01-05 22:48 ` Hugh Dickins
2018-01-06 4:54 ` Hanjun Guo
2018-01-06 6:06 ` Dave Hansen
2018-01-06 6:28 ` Hanjun Guo
2018-01-06 6:53 ` Hanjun Guo
2018-01-06 7:55 ` Dave Hansen
2018-01-06 8:42 ` Hanjun Guo
2018-01-06 7:51 ` Dave Hansen
2018-01-06 17:22 ` Andrea Arcangeli
2017-11-23 0:34 ` [PATCH 06/23] x86, kaiser: allow NX poison to be set in p4d/pgd Dave Hansen
2017-11-23 0:34 ` [PATCH 07/23] x86, kaiser: make sure static PGDs are 8k in size Dave Hansen
2017-11-23 0:34 ` [PATCH 08/23] x86, kaiser: map cpu entry area Dave Hansen
2017-11-23 0:34 ` [PATCH 09/23] x86, kaiser: map dynamically-allocated LDTs Dave Hansen
2017-11-23 19:42 ` Eric Biggers
2017-11-23 20:12 ` Andy Lutomirski
2017-11-23 0:34 ` [PATCH 10/23] x86, kaiser: map espfix structures Dave Hansen
2017-11-23 0:34 ` [PATCH 11/23] x86, kaiser: map entry stack variables Dave Hansen
2017-11-23 3:31 ` Andy Lutomirski
2017-11-23 15:37 ` Dave Hansen [this message]
2017-11-23 15:55 ` Andy Lutomirski
2017-11-23 0:35 ` [PATCH 12/23] x86, kaiser: map virtually-addressed performance monitoring buffers Dave Hansen
2017-11-23 0:35 ` [PATCH 13/23] x86, mm: Move CR3 construction functions Dave Hansen
2017-11-23 0:35 ` [PATCH 14/23] x86, mm: remove hard-coded ASID limit checks Dave Hansen
2017-11-23 0:35 ` [PATCH 15/23] x86, mm: put mmu-to-h/w ASID translation in one place Dave Hansen
2017-11-23 0:35 ` [PATCH 16/23] x86, pcid, kaiser: allow flushing for future ASID switches Dave Hansen
2017-11-23 0:35 ` [PATCH 17/23] x86, kaiser: use PCID feature to make user and kernel switches faster Dave Hansen
2017-11-23 0:35 ` [PATCH 18/23] x86, kaiser: disable native VSYSCALL Dave Hansen
2017-11-23 0:35 ` [PATCH 19/23] x86, kaiser: add debugfs file to turn KAISER on/off at runtime Dave Hansen
2017-11-23 0:35 ` [PATCH 20/23] x86, kaiser: add a function to check for KAISER being enabled Dave Hansen
2017-11-25 1:23 ` Eduardo Valentin
2017-11-23 0:35 ` [PATCH 21/23] x86, kaiser: un-poison PGDs at runtime Dave Hansen
2017-11-25 1:17 ` Eduardo Valentin
2017-11-23 0:35 ` [PATCH 22/23] x86, kaiser: allow KAISER to be enabled/disabled " Dave Hansen
2017-11-23 0:35 ` [PATCH 23/23] x86, kaiser: add Kconfig Dave Hansen
2017-11-23 7:23 ` [PATCH 00/23] [v4] KAISER: unmap most of the kernel from userspace page tables Ingo Molnar
2017-11-23 7:27 ` Ingo Molnar
2017-11-23 7:32 ` Ingo Molnar
2017-11-23 15:02 ` Dave Hansen
2017-11-23 16:20 ` Dave Hansen
2017-11-24 6:35 ` Ingo Molnar
2017-11-24 6:41 ` Dave Hansen
2017-11-24 7:33 ` Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ecccf06a-5791-f105-c080-01af351c0bc4@linux.intel.com \
--to=dave.hansen@linux.intel.com \
--cc=daniel.gruss@iaik.tugraz.at \
--cc=hughd@google.com \
--cc=keescook@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=michael.schwarz@iaik.tugraz.at \
--cc=moritz.lipp@iaik.tugraz.at \
--cc=richard.fellner@student.tugraz.at \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).