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From: Nadav Amit <namit@vmware.com>
To: Ingo Molnar <mingo@redhat.com>
Cc: <linux-kernel@vger.kernel.org>, <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>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Nadav Amit <namit@vmware.com>
Subject: [PATCH v3 3/7] x86/mm: temporary mm struct
Date: Fri, 2 Nov 2018 16:29:42 -0700	[thread overview]
Message-ID: <20181102232946.98461-4-namit@vmware.com> (raw)
In-Reply-To: <20181102232946.98461-1-namit@vmware.com>

From: Andy Lutomirski <luto@kernel.org>

Sometimes we want to set a temporary page-table entries (PTEs) in one of
the cores, without allowing other cores to use - even speculatively -
these mappings. There are two benefits for doing so:

(1) Security: if sensitive PTEs are set, temporary mm prevents their use
in other cores. This hardens the security as it prevents exploding a
dangling pointer to overwrite sensitive data using the sensitive PTE.

(2) Avoiding TLB shootdowns: the PTEs do not need to be flushed in
remote page-tables.

To do so a temporary mm_struct can be used. Mappings which are private
for this mm can be set in the userspace part of the address-space.
During the whole time in which the temporary mm is loaded, interrupts
must be disabled.

The first use-case for temporary PTEs, which will follow, is for poking
the kernel text.

[ Commit message was written by Nadav ]

Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/mmu_context.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 0ca50611e8ce..7cc8e5c50bf6 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -338,4 +338,24 @@ static inline unsigned long __get_current_cr3_fast(void)
 	return cr3;
 }
 
+typedef struct {
+	struct mm_struct *prev;
+} temporary_mm_state_t;
+
+static inline temporary_mm_state_t use_temporary_mm(struct mm_struct *mm)
+{
+	temporary_mm_state_t state;
+
+	lockdep_assert_irqs_disabled();
+	state.prev = this_cpu_read(cpu_tlbstate.loaded_mm);
+	switch_mm_irqs_off(NULL, mm, current);
+	return state;
+}
+
+static inline void unuse_temporary_mm(temporary_mm_state_t prev)
+{
+	lockdep_assert_irqs_disabled();
+	switch_mm_irqs_off(NULL, prev.prev, current);
+}
+
 #endif /* _ASM_X86_MMU_CONTEXT_H */
-- 
2.17.1


  parent reply	other threads:[~2018-11-02 23:32 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-02 23:29 [PATCH v3 0/7] x86/alternatives: text_poke() fixes Nadav Amit
2018-11-02 23:29 ` [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-11-03 10:11   ` Jiri Kosina
2018-11-04 20:58   ` Thomas Gleixner
2018-11-05 18:14     ` Nadav Amit
2018-11-02 23:29 ` [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init Nadav Amit
2018-11-05 12:39   ` Peter Zijlstra
2018-11-05 13:33     ` Peter Zijlstra
2018-11-05 14:09   ` Peter Zijlstra
2018-11-05 17:22     ` Andy Lutomirski
2018-11-05 17:49       ` Nadav Amit
2018-11-05 19:03         ` Andy Lutomirski
2018-11-05 19:25           ` Nadav Amit
2018-11-05 20:05             ` Andy Lutomirski
2018-11-05 20:28               ` Thomas Gleixner
2018-11-05 21:31                 ` Nadav Amit
2018-11-07 19:13     ` Nadav Amit
2018-11-08 10:41       ` Peter Zijlstra
2018-11-02 23:29 ` Nadav Amit [this message]
2018-11-02 23:29 ` [PATCH v3 4/7] fork: provide a function for copying init_mm Nadav Amit
2018-11-02 23:29 ` [PATCH v3 5/7] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-11-02 23:29 ` [PATCH v3 6/7] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-11-05 13:19   ` Peter Zijlstra
2018-11-05 13:30   ` Peter Zijlstra
2018-11-05 18:04     ` Nadav Amit
2018-11-06  8:20       ` Peter Zijlstra
2018-11-06 13:11         ` Peter Zijlstra
2018-11-06 18:11           ` Nadav Amit
2018-11-06 19:08             ` Peter Zijlstra
2018-11-02 23:29 ` [PATCH v3 7/7] x86/alternatives: remove text_poke() return value Nadav Amit

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