[v4,04/23] x86/mm: Save DRs when loading a temporary mm
diff mbox series

Message ID 20190422185805.1169-5-rick.p.edgecombe@intel.com
State New
Headers show
Series
  • Merge text_poke fixes and executable lockdowns
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Commit Message

Edgecombe, Rick P April 22, 2019, 6:57 p.m. UTC
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>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/include/asm/mmu_context.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

Comments

Borislav Petkov April 25, 2019, 4:36 p.m. UTC | #1
> Subject: Re: [PATCH v4 04/23] x86/mm: Save DRs when loading a temporary mm

s/DRs/debug registers/

On Mon, Apr 22, 2019 at 11:57:46AM -0700, 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

s/that //

> 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>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---
>  arch/x86/include/asm/mmu_context.h | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
Peter Zijlstra April 25, 2019, 6:17 p.m. UTC | #2
On Mon, Apr 22, 2019 at 11:57:46AM -0700, 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.

Ooh, goody, that would be fun indeed.

> Cc: Andy Lutomirski <luto@kernel.org>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> Signed-off-by: Nadav Amit <namit@vmware.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

Patch
diff mbox series

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index d684b954f3c0..81861862038a 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;
 
@@ -380,6 +381,21 @@  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.
+	 */
+	if (hw_breakpoint_active())
+		hw_breakpoint_disable();
+
 	return state;
 }
 
@@ -387,6 +403,13 @@  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 (hw_breakpoint_active())
+		hw_breakpoint_restore();
 }
 
 #endif /* _ASM_X86_MMU_CONTEXT_H */