From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Nadav Amit <nadav.amit@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
linux_dti@icloud.com, linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, akpm@linux-foundation.org,
kernel-hardening@lists.openwall.com, linux-mm@kvack.org,
will.deacon@arm.com, ard.biesheuvel@linaro.org,
kristen@linux.intel.com, deneen.t.dock@intel.com,
Nadav Amit <namit@vmware.com>
Subject: Re: [PATCH v3 03/20] x86/mm: Save DRs when loading a temporary mm
Date: Thu, 21 Feb 2019 16:07:31 -0800 [thread overview]
Message-ID: <20190222000731.GE7224@linux.intel.com> (raw)
In-Reply-To: <20190221234451.17632-4-rick.p.edgecombe@intel.com>
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().
> + if (state.bp_enabled)
> + hw_breakpoint_disable();
> +
> return state;
> }
>
> @@ -387,6 +405,13 @@ static inline void unuse_temporary_mm(temp_mm_state_t prev)
> {
> lockdep_assert_irqs_disabled();
> switch_mm_irqs_off(NULL, prev.prev, current);
> +
> + /*
> + * Restore the breakpoints if they were disabled before the temporary mm
> + * was loaded.
> + */
> + if (prev.bp_enabled)
> + hw_breakpoint_restore();
> }
>
> #endif /* _ASM_X86_MMU_CONTEXT_H */
> --
> 2.17.1
>
next prev parent reply other threads:[~2019-02-22 0:07 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 [this message]
2019-02-22 0:17 ` Nadav Amit
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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