From: Dave Hansen <dave.hansen@linux.intel.com> To: Borislav Petkov <bp@alien8.de> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, hughd@google.com, x86@kernel.org Subject: Re: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3 switching Date: Wed, 1 Nov 2017 11:27:48 -0700 [thread overview] Message-ID: <d991c9c0-ad36-929b-ae1b-05cc97aff19f@linux.intel.com> (raw) In-Reply-To: <20171101181805.3jjzfe6vhmgorjtp@pd.tnic> On 11/01/2017 11:18 AM, Borislav Petkov wrote: >> +.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req >> + movq %cr3, %r\scratch_reg >> + movq %r\scratch_reg, \save_reg > > So one of the args gets passed as "ax", for example, which then gets > completed to a register with the "%r" prepended and the other is a full > register: %r14. > > What for? Can we stick with one format pls? This allows for a tiny optimization of Andy's that I realize I must have blown away at some point. It lets us do a 32-bit-register instruction (and using %eXX) when checking KAISER_SWITCH_MASK instead of a 64-bit register via %rXX. I don't feel strongly about maintaining that optimization it looks weird and surely doesn't actually do much. >> diff -puN arch/x86/entry/entry_64_compat.S~kaiser-luto-base-cr3-work arch/x86/entry/entry_64_compat.S >> --- a/arch/x86/entry/entry_64_compat.S~kaiser-luto-base-cr3-work 2017-10-31 15:03:48.107007348 -0700 >> +++ b/arch/x86/entry/entry_64_compat.S 2017-10-31 15:03:48.113007631 -0700 >> @@ -48,8 +48,13 @@ >> ENTRY(entry_SYSENTER_compat) >> /* Interrupts are off on entry. */ >> SWAPGS_UNSAFE_STACK >> + >> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp >> >> + pushq %rdi >> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi >> + popq %rdi > > So we switch to kernel CR3 right after we've setup kernel stack... > >> + >> /* >> * User tracing code (ptrace or signal handlers) might assume that >> * the saved RAX contains a 32-bit number when we're invoking a 32-bit >> @@ -91,6 +96,9 @@ ENTRY(entry_SYSENTER_compat) >> pushq $0 /* pt_regs->r15 = 0 */ >> cld >> >> + pushq %rdi >> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi >> + popq %rdi > > ... and switch here *again*, after pushing pt_regs?!? What's up? > >> /* >> * SYSENTER doesn't filter flags, so we need to clear NT and AC >> * ourselves. To save a few cycles, we can check whether Thanks for catching that. We can kill one of these. I'm inclined to kill the first one. Looking at the second one since we've just saved off ptregs, that should make %rdi safe to clobber without the push/pop at all. Does that seem like it would work?
WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave.hansen@linux.intel.com> To: Borislav Petkov <bp@alien8.de> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, hughd@google.com, x86@kernel.org Subject: Re: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3 switching Date: Wed, 1 Nov 2017 11:27:48 -0700 [thread overview] Message-ID: <d991c9c0-ad36-929b-ae1b-05cc97aff19f@linux.intel.com> (raw) In-Reply-To: <20171101181805.3jjzfe6vhmgorjtp@pd.tnic> On 11/01/2017 11:18 AM, Borislav Petkov wrote: >> +.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req >> + movq %cr3, %r\scratch_reg >> + movq %r\scratch_reg, \save_reg > > So one of the args gets passed as "ax", for example, which then gets > completed to a register with the "%r" prepended and the other is a full > register: %r14. > > What for? Can we stick with one format pls? This allows for a tiny optimization of Andy's that I realize I must have blown away at some point. It lets us do a 32-bit-register instruction (and using %eXX) when checking KAISER_SWITCH_MASK instead of a 64-bit register via %rXX. I don't feel strongly about maintaining that optimization it looks weird and surely doesn't actually do much. >> diff -puN arch/x86/entry/entry_64_compat.S~kaiser-luto-base-cr3-work arch/x86/entry/entry_64_compat.S >> --- a/arch/x86/entry/entry_64_compat.S~kaiser-luto-base-cr3-work 2017-10-31 15:03:48.107007348 -0700 >> +++ b/arch/x86/entry/entry_64_compat.S 2017-10-31 15:03:48.113007631 -0700 >> @@ -48,8 +48,13 @@ >> ENTRY(entry_SYSENTER_compat) >> /* Interrupts are off on entry. */ >> SWAPGS_UNSAFE_STACK >> + >> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp >> >> + pushq %rdi >> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi >> + popq %rdi > > So we switch to kernel CR3 right after we've setup kernel stack... > >> + >> /* >> * User tracing code (ptrace or signal handlers) might assume that >> * the saved RAX contains a 32-bit number when we're invoking a 32-bit >> @@ -91,6 +96,9 @@ ENTRY(entry_SYSENTER_compat) >> pushq $0 /* pt_regs->r15 = 0 */ >> cld >> >> + pushq %rdi >> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi >> + popq %rdi > > ... and switch here *again*, after pushing pt_regs?!? What's up? > >> /* >> * SYSENTER doesn't filter flags, so we need to clear NT and AC >> * ourselves. To save a few cycles, we can check whether Thanks for catching that. We can kill one of these. I'm inclined to kill the first one. Looking at the second one since we've just saved off ptregs, that should make %rdi safe to clobber without the push/pop at all. Does that seem like it would work? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-11-01 18:27 UTC|newest] Thread overview: 204+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-31 22:31 [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-10-31 22:31 ` [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3 switching Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-11-01 0:43 ` Brian Gerst 2017-11-01 0:43 ` Brian Gerst 2017-11-01 1:08 ` Dave Hansen 2017-11-01 1:08 ` Dave Hansen 2017-11-01 18:18 ` Borislav Petkov 2017-11-01 18:18 ` Borislav Petkov 2017-11-01 18:27 ` Dave Hansen [this message] 2017-11-01 18:27 ` Dave Hansen 2017-11-01 20:42 ` Borislav Petkov 2017-11-01 20:42 ` Borislav Petkov 2017-11-01 21:01 ` Thomas Gleixner 2017-11-01 21:01 ` Thomas Gleixner 2017-11-01 22:58 ` Dave Hansen 2017-11-01 22:58 ` Dave Hansen 2017-10-31 22:31 ` [PATCH 02/23] x86, kaiser: do not set _PAGE_USER for init_mm page tables Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-11-01 21:11 ` Thomas Gleixner 2017-11-01 21:11 ` Thomas Gleixner 2017-11-01 21:24 ` Andy Lutomirski 2017-11-01 21:24 ` Andy Lutomirski 2017-11-01 21:28 ` Thomas Gleixner 2017-11-01 21:28 ` Thomas Gleixner 2017-11-01 21:52 ` Dave Hansen 2017-11-01 21:52 ` Dave Hansen 2017-11-01 22:11 ` Thomas Gleixner 2017-11-01 22:11 ` Thomas Gleixner 2017-11-01 22:12 ` Linus Torvalds 2017-11-01 22:12 ` Linus Torvalds 2017-11-01 22:20 ` Thomas Gleixner 2017-11-01 22:20 ` Thomas Gleixner 2017-11-01 22:45 ` Kees Cook 2017-11-01 22:45 ` Kees Cook 2017-11-02 7:10 ` Andy Lutomirski 2017-11-02 7:10 ` Andy Lutomirski 2017-11-02 11:33 ` Thomas Gleixner 2017-11-02 11:33 ` Thomas Gleixner 2017-11-02 11:59 ` Andy Lutomirski 2017-11-02 11:59 ` Andy Lutomirski 2017-11-02 12:56 ` Thomas Gleixner 2017-11-02 12:56 ` Thomas Gleixner 2017-11-02 16:38 ` Dave Hansen 2017-11-02 16:38 ` Dave Hansen 2017-11-02 18:19 ` Andy Lutomirski 2017-11-02 18:19 ` Andy Lutomirski 2017-11-02 18:24 ` Thomas Gleixner 2017-11-02 18:24 ` Thomas Gleixner 2017-11-02 18:24 ` Linus Torvalds 2017-11-02 18:24 ` Linus Torvalds 2017-11-02 18:40 ` Thomas Gleixner 2017-11-02 18:40 ` Thomas Gleixner 2017-11-02 18:57 ` Linus Torvalds 2017-11-02 18:57 ` Linus Torvalds 2017-11-02 21:41 ` Thomas Gleixner 2017-11-02 21:41 ` Thomas Gleixner 2017-11-02 7:07 ` Andy Lutomirski 2017-11-02 7:07 ` Andy Lutomirski 2017-11-02 11:21 ` Thomas Gleixner 2017-11-02 11:21 ` Thomas Gleixner 2017-10-31 22:31 ` [PATCH 03/23] x86, kaiser: disable global pages Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-11-01 21:18 ` Thomas Gleixner 2017-11-01 21:18 ` Thomas Gleixner 2017-11-01 22:12 ` Dave Hansen 2017-11-01 22:12 ` Dave Hansen 2017-11-01 22:28 ` Thomas Gleixner 2017-11-01 22:28 ` Thomas Gleixner 2017-10-31 22:31 ` [PATCH 04/23] x86, tlb: make CR4-based TLB flushes more robust Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-11-01 8:01 ` Andy Lutomirski 2017-11-01 8:01 ` Andy Lutomirski 2017-11-01 10:11 ` Kirill A. Shutemov 2017-11-01 10:11 ` Kirill A. Shutemov 2017-11-01 10:38 ` Andy Lutomirski 2017-11-01 10:38 ` Andy Lutomirski 2017-11-01 10:56 ` Kirill A. Shutemov 2017-11-01 10:56 ` Kirill A. Shutemov 2017-11-01 11:18 ` Andy Lutomirski 2017-11-01 11:18 ` Andy Lutomirski 2017-11-01 22:21 ` Dave Hansen 2017-11-01 22:21 ` Dave Hansen 2017-11-01 21:25 ` Thomas Gleixner 2017-11-01 21:25 ` Thomas Gleixner 2017-11-01 22:24 ` Dave Hansen 2017-11-01 22:24 ` Dave Hansen 2017-11-01 22:30 ` Thomas Gleixner 2017-11-01 22:30 ` Thomas Gleixner 2017-10-31 22:31 ` [PATCH 05/23] x86, mm: document X86_CR4_PGE toggling behavior Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-10-31 23:31 ` Kees Cook 2017-10-31 23:31 ` Kees Cook 2017-10-31 22:31 ` [PATCH 06/23] x86, kaiser: introduce user-mapped percpu areas Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-11-01 21:47 ` Thomas Gleixner 2017-11-01 21:47 ` Thomas Gleixner 2017-10-31 22:31 ` [PATCH 07/23] x86, kaiser: unmap kernel from userspace page tables (core patch) Dave Hansen 2017-10-31 22:31 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 08/23] x86, kaiser: only populate shadow page tables for userspace Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 23:35 ` Kees Cook 2017-10-31 23:35 ` Kees Cook 2017-10-31 22:32 ` [PATCH 09/23] x86, kaiser: allow NX to be set in p4d/pgd Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 10/23] x86, kaiser: make sure static PGDs are 8k in size Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 11/23] x86, kaiser: map GDT into user page tables Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 12/23] x86, kaiser: map dynamically-allocated LDTs Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-11-01 8:00 ` Andy Lutomirski 2017-11-01 8:00 ` Andy Lutomirski 2017-11-01 8:06 ` Ingo Molnar 2017-11-01 8:06 ` Ingo Molnar 2017-10-31 22:32 ` [PATCH 13/23] x86, kaiser: map espfix structures Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 14/23] x86, kaiser: map entry stack variables Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 15/23] x86, kaiser: map trace interrupt entry Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 16/23] x86, kaiser: map debug IDT tables Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 17/23] x86, kaiser: map virtually-addressed performance monitoring buffers Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 18/23] x86, mm: Move CR3 construction functions Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 19/23] x86, mm: remove hard-coded ASID limit checks Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 20/23] x86, mm: put mmu-to-h/w ASID translation in one place Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 21/23] x86, pcid, kaiser: allow flushing for future ASID switches Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-11-01 8:03 ` Andy Lutomirski 2017-11-01 8:03 ` Andy Lutomirski 2017-11-01 14:17 ` Dave Hansen 2017-11-01 14:17 ` Dave Hansen 2017-11-01 20:31 ` Andy Lutomirski 2017-11-01 20:31 ` Andy Lutomirski 2017-11-01 20:59 ` Dave Hansen 2017-11-01 20:59 ` Dave Hansen 2017-11-01 21:04 ` Andy Lutomirski 2017-11-01 21:04 ` Andy Lutomirski 2017-11-01 21:06 ` Dave Hansen 2017-11-01 21:06 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 22/23] x86, kaiser: use PCID feature to make user and kernel switches faster Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 22:32 ` [PATCH 23/23] x86, kaiser: add Kconfig Dave Hansen 2017-10-31 22:32 ` Dave Hansen 2017-10-31 23:59 ` Kees Cook 2017-10-31 23:59 ` Kees Cook 2017-11-01 9:07 ` Borislav Petkov 2017-11-01 9:07 ` Borislav Petkov 2017-10-31 23:27 ` [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables Linus Torvalds 2017-10-31 23:27 ` Linus Torvalds 2017-10-31 23:44 ` Dave Hansen 2017-10-31 23:44 ` Dave Hansen 2017-11-01 0:21 ` Dave Hansen 2017-11-01 0:21 ` Dave Hansen 2017-11-01 7:59 ` Andy Lutomirski 2017-11-01 7:59 ` Andy Lutomirski 2017-11-01 16:08 ` Linus Torvalds 2017-11-01 16:08 ` Linus Torvalds 2017-11-01 17:31 ` Dave Hansen 2017-11-01 17:58 ` Randy Dunlap 2017-11-01 17:58 ` Randy Dunlap 2017-11-01 18:27 ` Linus Torvalds 2017-11-01 18:27 ` Linus Torvalds 2017-11-01 18:46 ` Dave Hansen 2017-11-01 18:46 ` Dave Hansen 2017-11-01 19:05 ` Linus Torvalds 2017-11-01 19:05 ` Linus Torvalds 2017-11-01 20:33 ` Andy Lutomirski 2017-11-01 20:33 ` Andy Lutomirski 2017-11-02 7:32 ` Andy Lutomirski 2017-11-02 7:32 ` Andy Lutomirski 2017-11-02 7:54 ` Andy Lutomirski 2017-11-02 7:54 ` Andy Lutomirski 2017-11-01 15:53 ` Dave Hansen 2017-11-01 15:53 ` Dave Hansen 2017-11-01 8:54 ` Ingo Molnar 2017-11-01 8:54 ` Ingo Molnar 2017-11-01 14:09 ` Thomas Gleixner 2017-11-01 14:09 ` Thomas Gleixner 2017-11-01 22:14 ` Dave Hansen 2017-11-01 22:14 ` Dave Hansen 2017-11-01 22:28 ` Linus Torvalds 2017-11-01 22:28 ` Linus Torvalds 2017-11-02 8:03 ` Peter Zijlstra 2017-11-02 8:03 ` Peter Zijlstra 2017-11-03 11:07 ` Kirill A. Shutemov 2017-11-03 11:07 ` Kirill A. Shutemov 2017-11-02 19:01 ` Will Deacon 2017-11-02 19:01 ` Will Deacon 2017-11-02 19:01 ` Will Deacon 2017-11-02 19:38 ` Dave Hansen 2017-11-02 19:38 ` Dave Hansen 2017-11-02 19:38 ` Dave Hansen 2017-11-03 13:41 ` Will Deacon 2017-11-03 13:41 ` Will Deacon 2017-11-03 13:41 ` Will Deacon 2017-11-22 16:19 ` Pavel Machek 2017-11-23 10:47 ` Pavel Machek
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