From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH 08/24] x86/entry: Add C version of SWAPGS and SWAPGS_UNSAFE_STACK
Date: Mon, 9 Nov 2020 19:04:49 +0100 [thread overview]
Message-ID: <c5485ba4-3652-8c98-c485-918d322c015e@oracle.com> (raw)
In-Reply-To: <CALCETrXtqC9w5gAa=UcF=B4z7vKuUL2sutsCJOjaSCK4CX4q0Q@mail.gmail.com>
On 11/9/20 6:38 PM, Andy Lutomirski wrote:
> On Mon, Nov 9, 2020 at 3:22 AM Alexandre Chartre
> <alexandre.chartre@oracle.com> wrote:
>>
>> SWAPGS and SWAPGS_UNSAFE_STACK are assembly macros. Add C versions
>> of these macros (swapgs() and swapgs_unsafe_stack()).
>
> This needs a very good justification. It also needs some kind of
> static verification that these helpers are only used by noinstr code,
> and they need to be __always_inline. And I cannot fathom how C code
> could possibly use SWAPGS_UNSAFE_STACK in a meaningful way.
>
You're right, I probably need to revisit the usage of SWAPGS_UNSAFE_STACK
in C code, that doesn't make sense. Looks like only SWAPGS is then needed.
Or maybe we can just use native_swapgs() instead?
I have added a C version of SWAPGS for moving paranoid_entry() to C because,
in this function, we need to switch CR3 before doing the updating GS. But I
really wonder if we need a paravirt swapgs here, and we can probably just use
native_swapgs().
Also, if we map the per cpu offsets (__per_cpu_offset) in the user page-table
then we will be able to update GS before switching CR3. That way we can keep the
GS update in assembly code, and just do the CR3 switch in C code. This would also
avoid having to disable stack-protector (patch 21).
alex.
next prev parent reply other threads:[~2020-11-09 18:02 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-09 11:22 [RFC][PATCH 00/24] x86/pti: Defer CR3 switch to C code Alexandre Chartre
2020-11-09 11:22 ` [RFC][PATCH 01/24] x86/syscall: Add wrapper for invoking syscall function Alexandre Chartre
2020-11-09 17:25 ` Andy Lutomirski
2020-11-09 17:45 ` Alexandre Chartre
2020-11-09 11:22 ` [RFC][PATCH 02/24] x86/entry: Update asm_call_on_stack to support more function arguments Alexandre Chartre
2020-11-09 11:22 ` [RFC][PATCH 03/24] x86/entry: Consolidate IST entry from userspace Alexandre Chartre
2020-11-09 11:22 ` [RFC][PATCH 04/24] x86/sev-es: Define a setup stack function for the VC idtentry Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 05/24] x86/entry: Implement ret_from_fork body with C code Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 06/24] x86/pti: Provide C variants of PTI switch CR3 macros Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 07/24] x86/entry: Fill ESPFIX stack using C code Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 08/24] x86/entry: Add C version of SWAPGS and SWAPGS_UNSAFE_STACK Alexandre Chartre
2020-11-09 17:38 ` Andy Lutomirski
2020-11-09 18:04 ` Alexandre Chartre [this message]
2020-11-09 11:23 ` [RFC][PATCH 09/24] x86/entry: Add C version of paranoid_entry/exit Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 10/24] x86/pti: Introduce per-task PTI trampoline stack Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 11/24] x86/pti: Function to clone page-table entries from a specified mm Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 12/24] x86/pti: Function to map per-cpu page-table entry Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 13/24] x86/pti: Extend PTI user mappings Alexandre Chartre
2020-11-09 17:28 ` Andy Lutomirski
2020-11-09 17:52 ` Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 14/24] x86/pti: Use PTI stack instead of trampoline stack Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 15/24] x86/pti: Execute syscall functions on the kernel stack Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 16/24] x86/pti: Execute IDT handlers " Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 17/24] x86/pti: Execute IDT handlers with error code " Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 18/24] x86/pti: Execute system vector handlers " Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 19/24] x86/pti: Execute page fault handler " Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 20/24] x86/pti: Execute NMI " Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 21/24] x86/entry: Disable stack-protector for IST entry C handlers Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 22/24] x86/entry: Defer paranoid entry/exit to C code Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 23/24] x86/entry: Remove paranoid_entry and paranoid_exit Alexandre Chartre
2020-11-09 11:23 ` [RFC][PATCH 24/24] x86/pti: Defer CR3 switch to C code for non-IST and syscall entries Alexandre Chartre
2020-11-09 14:00 ` [RFC][PATCH 00/24] x86/pti: Defer CR3 switch to C code Alexandre Chartre
2020-11-09 14:44 Alexandre Chartre
2020-11-09 14:44 ` [RFC][PATCH 08/24] x86/entry: Add C version of SWAPGS and SWAPGS_UNSAFE_STACK Alexandre Chartre
2020-11-09 19:55 ` Alexandre Chartre
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