From: Thomas Gleixner <tglx@linutronix.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@amacapital.net>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 15/43] x86/entry/64: Create a percpu SYSCALL entry trampoline
Date: Fri, 24 Nov 2017 14:52:49 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1711241451350.1757@nanos> (raw)
In-Reply-To: <20171124091448.7649-16-mingo@kernel.org>
On Fri, 24 Nov 2017, Ingo Molnar wrote:
> From: Andy Lutomirski <luto@kernel.org>
>
> Handling SYSCALL is tricky: the SYSCALL handler is entered with every
> single register (except FLAGS), including RSP, live. It somehow needs
> to set RSP to point to a valid stack, which means it needs to save the
> user RSP somewhere and find its own stack pointer. The canonical way
> to do this is with SWAPGS, which lets us access percpu data using the
> %gs prefix.
>
> With KAISER-like pagetable switching, this is problematic. Without a
> scratch register, switching CR3 is impossible, so %gs-based percpu
> memory would need to be mapped in the user pagetables. Doing that
> without information leaks is difficult or impossible.
>
> Instead, use a different sneaky trick. Map a copy of the first part
> of the SYSCALL asm at a different address for each CPU. Now RIP
> varies depending on the CPU, so we can use RIP-relative memory access
> to access percpu memory. By putting the relevant information (one
> scratch slot and the stack address) at a constant offset relative to
> RIP, we can make SYSCALL work without relying on %gs.
Smart!
> A nice thing about this approach is that we can easily switch it on
> and off if we want pagetable switching to be configurable.
>
> The compat variant of SYSCALL doesn't have this problem in the first
> place -- there are plenty of scratch registers, since we don't care
> about preserving r8-r15. This patch therefore doesn't touch SYSCALL32
> at all.
>
> XXX: Whenever we settle how KAISER gets turned on and off, we should do
> the same to this.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
next prev parent reply other threads:[~2017-11-24 13:52 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-24 9:14 [PATCH 00/43] x86 entry-stack and Kaiser series, 2017/11/24 version Ingo Molnar
2017-11-24 9:14 ` [PATCH 01/43] x86/decoder: Add new TEST instruction pattern Ingo Molnar
2017-11-24 10:38 ` Borislav Petkov
2017-12-02 7:39 ` Robert Elliott (Persistent Memory)
2017-11-24 9:14 ` [PATCH 02/43] x86/entry/64: Allocate and enable the SYSENTER stack Ingo Molnar
2017-11-24 9:14 ` [PATCH 03/43] x86/dumpstack: Add get_stack_info() support for " Ingo Molnar
2017-11-24 9:14 ` [PATCH 04/43] x86/gdt: Put per-cpu GDT remaps in ascending order Ingo Molnar
2017-11-24 9:14 ` [PATCH 05/43] x86/fixmap: Generalize the GDT fixmap mechanism Ingo Molnar
2017-11-24 11:00 ` Borislav Petkov
2017-11-24 9:14 ` [PATCH 06/43] x86/kasan/64: Teach KASAN about the cpu_entry_area Ingo Molnar
2017-11-24 9:14 ` [PATCH 07/43] x86/entry: Fix assumptions that the HW TSS is at the beginning of cpu_tss Ingo Molnar
2017-11-24 9:14 ` [PATCH 08/43] x86/dumpstack: Handle stack overflow on all stacks Ingo Molnar
2017-11-24 9:14 ` [PATCH 09/43] x86/entry: Move SYSENTER_stack to the beginning of struct tss_struct Ingo Molnar
2017-11-24 11:44 ` Borislav Petkov
2017-11-24 9:14 ` [PATCH 10/43] x86/entry: Remap the TSS into the cpu entry area Ingo Molnar
2017-11-24 9:14 ` [PATCH 11/43] x86/entry/64: Separate cpu_current_top_of_stack from TSS.sp0 Ingo Molnar
2017-11-24 14:19 ` Borislav Petkov
2017-11-24 9:14 ` [PATCH 12/43] x86/espfix/64: Stop assuming that pt_regs is on the entry stack Ingo Molnar
2017-11-24 9:14 ` [PATCH 13/43] x86/entry/64: Use a percpu trampoline stack for IDT entries Ingo Molnar
2017-11-24 11:27 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 14/43] x86/entry/64: Return to userspace from the trampoline stack Ingo Molnar
2017-11-24 13:46 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 15/43] x86/entry/64: Create a percpu SYSCALL entry trampoline Ingo Molnar
2017-11-24 13:52 ` Thomas Gleixner [this message]
2017-11-24 9:14 ` [PATCH 16/43] x86/irq: Remove an old outdated comment about context tracking races Ingo Molnar
2017-11-24 13:53 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 17/43] x86/irq/64: Print the offending IP in the stack overflow warning Ingo Molnar
2017-11-24 14:22 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 18/43] x86/entry/64: Move the IST stacks into cpu_entry_area Ingo Molnar
2017-11-24 14:23 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 19/43] x86/entry/64: Remove the SYSENTER stack canary Ingo Molnar
2017-11-24 14:23 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 20/43] x86/entry: Clean up SYSENTER_stack code Ingo Molnar
2017-11-24 14:24 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 21/43] x86/mm/kaiser: Disable global pages by default with KAISER Ingo Molnar
2017-11-24 9:14 ` [PATCH 22/43] x86/mm/kaiser: Prepare assembly for entry/exit CR3 switching Ingo Molnar
2017-11-24 12:05 ` Peter Zijlstra
2017-11-24 12:17 ` Ingo Molnar
2017-11-24 12:45 ` Peter Zijlstra
2017-11-24 13:04 ` Thomas Gleixner
2017-11-24 9:14 ` [PATCH 23/43] x86/mm/kaiser: Introduce user-mapped per-cpu areas Ingo Molnar
2017-11-24 9:14 ` [PATCH 24/43] x86/mm/kaiser: Mark per-cpu data structures required for entry/exit Ingo Molnar
2017-11-24 9:14 ` [PATCH 25/43] x86/mm/kaiser: Unmap kernel from userspace page tables (core patch) Ingo Molnar
2017-11-24 12:13 ` Peter Zijlstra
2017-11-24 13:46 ` Ingo Molnar
2017-11-24 12:16 ` Peter Zijlstra
2017-11-24 16:33 ` Dave Hansen
2017-11-26 15:13 ` Ingo Molnar
2017-11-24 13:30 ` Peter Zijlstra
2017-11-26 15:15 ` Ingo Molnar
2017-11-27 8:59 ` [PATCH] x86/mm/kaiser: Use the other page_table_lock pattern Peter Zijlstra
2017-11-27 8:59 ` [PATCH] mm: Unify page_table_lock allocation pattern Peter Zijlstra
2017-11-24 9:14 ` [PATCH 26/43] x86/mm/kaiser: Allow NX poison to be set in p4d/pgd Ingo Molnar
2017-11-24 9:14 ` [PATCH 27/43] x86/mm/kaiser: Make sure static PGDs are 8k in size Ingo Molnar
2017-11-24 9:14 ` [PATCH 28/43] x86/mm/kaiser: Map CPU entry area Ingo Molnar
2017-11-24 13:43 ` Peter Zijlstra
2017-11-24 9:14 ` [PATCH 29/43] x86/mm/kaiser: Map dynamically-allocated LDTs Ingo Molnar
2017-11-24 9:14 ` [PATCH 30/43] x86/mm/kaiser: Map espfix structures Ingo Molnar
2017-11-24 13:47 ` Peter Zijlstra
2017-11-24 16:17 ` Andy Lutomirski
2017-11-27 9:14 ` Peter Zijlstra
2017-11-27 15:35 ` Peter Zijlstra
2017-11-24 9:14 ` [PATCH 31/43] x86/mm/kaiser: Map entry stack variable Ingo Molnar
2017-11-24 9:14 ` [PATCH 32/43] x86/mm/kaiser: Map virtually-addressed performance monitoring buffers Ingo Molnar
2017-11-24 9:14 ` [PATCH 33/43] x86/mm: Move CR3 construction functions Ingo Molnar
2017-11-24 9:14 ` [PATCH 34/43] x86/mm: Remove hard-coded ASID limit checks Ingo Molnar
2017-11-24 9:14 ` [PATCH 35/43] x86/mm: Put mmu-to-h/w ASID translation in one place Ingo Molnar
2017-11-24 9:14 ` [PATCH 36/43] x86/mm: Allow flushing for future ASID switches Ingo Molnar
2017-11-24 9:14 ` [PATCH 37/43] x86/mm/kaiser: Use PCID feature to make user and kernel switches faster Ingo Molnar
2017-11-24 9:14 ` [PATCH 38/43] x86/mm/kaiser: Disable native VSYSCALL Ingo Molnar
2017-11-24 9:14 ` [PATCH 39/43] x86/mm/kaiser: Add debugfs file to turn KAISER on/off at runtime Ingo Molnar
2017-11-24 9:14 ` [PATCH 40/43] x86/mm/kaiser: Add a function to check for KAISER being enabled Ingo Molnar
2017-11-24 9:14 ` [PATCH 41/43] x86/mm/kaiser: Un-poison PGDs at runtime Ingo Molnar
2017-11-24 9:14 ` [PATCH 42/43] x86/mm/kaiser: Allow KAISER to be enabled/disabled " Ingo Molnar
2017-11-24 9:14 ` [PATCH 43/43] x86/mm/kaiser: Add Kconfig Ingo Molnar
2017-11-24 13:55 ` [PATCH 00/43] x86 entry-stack and Kaiser series, 2017/11/24 version Ingo Molnar
2017-11-24 15:23 ` Thomas Gleixner
2017-11-24 17:19 ` Ingo Molnar
2017-11-24 17:23 [PATCH 00/43] x86 entry-stack and Kaiser series, 2017/11/24, v2 version Ingo Molnar
2017-11-24 17:23 ` [PATCH 15/43] x86/entry/64: Create a percpu SYSCALL entry trampoline Ingo Molnar
2017-11-25 11:40 ` Borislav Petkov
2017-11-25 15:00 ` Andy Lutomirski
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