| Message ID | 20190422185805.1169-5-rick.p.edgecombe@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Merge text_poke fixes and executable lockdowns | expand |
> 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(+)
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>
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 */