From: Nadav Amit <namit@vmware.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Damian Tometzki <linux_dti@icloud.com>,
linux-integrity <linux-integrity@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Linux-MM <linux-mm@kvack.org>, Will Deacon <will.deacon@arm.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
"deneen.t.dock@intel.com" <deneen.t.dock@intel.com>
Subject: Re: [PATCH v3 03/20] x86/mm: Save DRs when loading a temporary mm
Date: Fri, 22 Feb 2019 00:17:24 +0000 [thread overview]
Message-ID: <A8727670-F848-4BAD-BEFE-9C94329EA774@vmware.com> (raw)
In-Reply-To: <20190222000731.GE7224@linux.intel.com>
> On Feb 21, 2019, at 4:07 PM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
>
> On Thu, Feb 21, 2019 at 03:44:34PM -0800, Rick Edgecombe wrote:
>> From: Nadav Amit <namit@vmware.com>
>>
>> Prevent user watchpoints from mistakenly firing while the temporary mm
>> is being used. As the addresses that of the temporary mm might overlap
>> those of the user-process, this is necessary to prevent wrong signals
>> or worse things from happening.
>>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Signed-off-by: Nadav Amit <namit@vmware.com>
>> ---
>> arch/x86/include/asm/mmu_context.h | 25 +++++++++++++++++++++++++
>> 1 file changed, 25 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
>> index d684b954f3c0..0d6c72ece750 100644
>> --- a/arch/x86/include/asm/mmu_context.h
>> +++ b/arch/x86/include/asm/mmu_context.h
>> @@ -13,6 +13,7 @@
>> #include <asm/tlbflush.h>
>> #include <asm/paravirt.h>
>> #include <asm/mpx.h>
>> +#include <asm/debugreg.h>
>>
>> extern atomic64_t last_mm_ctx_id;
>>
>> @@ -358,6 +359,7 @@ static inline unsigned long __get_current_cr3_fast(void)
>>
>> typedef struct {
>> struct mm_struct *prev;
>> + unsigned short bp_enabled : 1;
>> } temp_mm_state_t;
>>
>> /*
>> @@ -380,6 +382,22 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
>> lockdep_assert_irqs_disabled();
>> state.prev = this_cpu_read(cpu_tlbstate.loaded_mm);
>> switch_mm_irqs_off(NULL, mm, current);
>> +
>> + /*
>> + * If breakpoints are enabled, disable them while the temporary mm is
>> + * used. Userspace might set up watchpoints on addresses that are used
>> + * in the temporary mm, which would lead to wrong signals being sent or
>> + * crashes.
>> + *
>> + * Note that breakpoints are not disabled selectively, which also causes
>> + * kernel breakpoints (e.g., perf's) to be disabled. This might be
>> + * undesirable, but still seems reasonable as the code that runs in the
>> + * temporary mm should be short.
>> + */
>> + state.bp_enabled = hw_breakpoint_active();
>
> Pretty sure caching hw_breakpoint_active() is unnecessary. It queries a
> per-cpu value, not hardware's DR7 register, and that same value is
> consumed by hw_breakpoint_restore(). No idea if breakpoints can be
> disabled while using a temp mm, but even if that can happen, there's no
> need to restore breakpoints if they've all been disabled, i.e. if
> hw_breakpoint_active() returns false in unuse_temporary_mm().
Good point. I will fix it for next version.
Thanks,
Nadav
next prev parent reply other threads:[~2019-02-22 0:17 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 23:44 [PATCH v3 00/20] Merge text_poke fixes and executable lockdowns Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 01/20] x86/jump_label: Use text_poke_early() during early init Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 02/20] x86/mm: Introduce temporary mm structs Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 03/20] x86/mm: Save DRs when loading a temporary mm Rick Edgecombe
2019-02-22 0:07 ` Sean Christopherson
2019-02-22 0:17 ` Nadav Amit [this message]
2019-02-21 23:44 ` [PATCH v3 04/20] fork: Provide a function for copying init_mm Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 05/20] x86/alternative: Initialize temporary mm for patching Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 06/20] x86/alternative: Use temporary mm for text poking Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 07/20] x86/kgdb: Avoid redundant comparison of patched code Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 08/20] x86/ftrace: Set trampoline pages as executable Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 09/20] x86/kprobes: Set instruction page " Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 10/20] x86/module: Avoid breaking W^X while loading modules Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 11/20] x86/jump-label: Remove support for custom poker Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 12/20] x86/alternative: Remove the return value of text_poke_*() Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 13/20] x86/mm/cpa: Add set_direct_map_ functions Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 14/20] mm: Make hibernate handle unmapped pages Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 15/20] vmalloc: Add flag for free of special permsissions Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 16/20] modules: Use vmalloc special flag Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 17/20] bpf: " Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 18/20] x86/ftrace: " Rick Edgecombe
2019-02-22 0:22 ` Steven Rostedt
2019-02-22 0:55 ` Edgecombe, Rick P
2019-02-21 23:44 ` [PATCH v3 19/20] x86/kprobes: " Rick Edgecombe
2019-02-21 23:44 ` [PATCH v3 20/20] x86/alternative: Comment about module removal races Rick Edgecombe
2019-02-22 16:14 ` [PATCH v3 00/20] Merge text_poke fixes and executable lockdowns Borislav Petkov
2019-02-22 18:32 ` Edgecombe, Rick P
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