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From: Nadav Amit <namit@vmware.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
	<x86@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	<linux-arch@vger.kernel.org>, Andy Lutomirski <luto@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nadav Amit <namit@vmware.com>
Subject: [RFC PATCH 2/6] x86/mm: temporary mm struct
Date: Wed, 29 Aug 2018 01:11:43 -0700	[thread overview]
Message-ID: <20180829081147.184610-3-namit@vmware.com> (raw)
In-Reply-To: <20180829081147.184610-1-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: Andy Lutomirski <luto@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.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 eeeb9289c764..96afc8c0cf15 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:[~2018-08-29  8:13 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-29  8:11 [RFC PATCH 0/6] x86: text_poke() fixes Nadav Amit
2018-08-29  8:11 ` [RFC PATCH 1/6] x86/alternative: assert text_mutex is taken Nadav Amit
2018-08-29  8:59   ` Masami Hiramatsu
2018-08-29 17:11     ` Nadav Amit
2018-08-29 19:36       ` Nadav Amit
2018-08-29 20:13         ` Sean Christopherson
2018-08-29 20:44           ` Nadav Amit
2018-08-29 21:00             ` Sean Christopherson
2018-08-29 22:56               ` Nadav Amit
2018-08-30  2:26               ` Masami Hiramatsu
2018-08-30  5:23                 ` Nadav Amit
2018-08-29  8:11 ` Nadav Amit [this message]
2018-08-29  9:49   ` [RFC PATCH 2/6] x86/mm: temporary mm struct Masami Hiramatsu
2018-08-29 15:41     ` Andy Lutomirski
2018-08-29 16:54       ` Nadav Amit
2018-08-29 21:38         ` Andy Lutomirski
2018-08-30  1:38       ` Masami Hiramatsu
2018-08-30  1:59         ` Andy Lutomirski
2018-08-31  4:42           ` Masami Hiramatsu
2018-08-29 15:46   ` Andy Lutomirski
2018-08-29  8:11 ` [RFC PATCH 3/6] fork: provide a function for copying init_mm Nadav Amit
2018-08-29  9:54   ` Masami Hiramatsu
2018-08-29  8:11 ` [RFC PATCH 4/6] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-08-29 13:21   ` Masami Hiramatsu
2018-08-29 17:45     ` Nadav Amit
2018-08-29  8:11 ` [RFC PATCH 5/6] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-08-29  9:28   ` Peter Zijlstra
2018-08-29 15:46     ` Andy Lutomirski
2018-08-29 16:14       ` Peter Zijlstra
2018-08-29 16:32         ` Andy Lutomirski
2018-08-29 16:37           ` Dave Hansen
2018-08-29  8:11 ` [RFC PATCH 6/6] x86/alternatives: remove text_poke() return value Nadav Amit
2018-08-29  9:52   ` Masami Hiramatsu
2018-08-29 17:15     ` Nadav Amit

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