Commit-ID: d97080ebed7811a53c931032a284166ee46b9565 Gitweb: https://git.kernel.org/tip/d97080ebed7811a53c931032a284166ee46b9565 Author: Nadav Amit <na...@vmware.com> AuthorDate: Thu, 25 Apr 2019 17:11:24 -0700 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Tue, 30 Apr 2019 12:37:50 +0200
x86/mm: Save debug registers when loading a temporary mm Prevent user watchpoints from mistakenly firing while the temporary mm is being used. As the addresses of the temporary mm might overlap those of the user-process, this is necessary to prevent wrong signals or worse things from happening. Signed-off-by: Nadav Amit <na...@vmware.com> Signed-off-by: Rick Edgecombe <rick.p.edgeco...@intel.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: <a...@linux-foundation.org> Cc: <ard.biesheu...@linaro.org> Cc: <deneen.t.d...@intel.com> Cc: <kernel-harden...@lists.openwall.com> Cc: <kris...@linux.intel.com> Cc: <linux_...@icloud.com> Cc: <will.dea...@arm.com> Cc: Andy Lutomirski <l...@kernel.org> Cc: Borislav Petkov <b...@alien8.de> Cc: Dave Hansen <dave.han...@linux.intel.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Rik van Riel <r...@surriel.com> Cc: Thomas Gleixner <t...@linutronix.de> Link: https://lkml.kernel.org/r/20190426001143.4983-5-na...@vmware.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/include/asm/mmu_context.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 24dc3b810970..93dff1963337 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(); temp_state.mm = 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 temp_state; } @@ -387,6 +403,13 @@ static inline void unuse_temporary_mm(temp_mm_state_t prev_state) { lockdep_assert_irqs_disabled(); switch_mm_irqs_off(NULL, prev_state.mm, 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 */
