From: Juergen Gross jgross@suse.com
[ Upstream commit abee7c494d8c41bb388839bccc47e06247f0d7de ]
When running in lazy TLB mode the currently active page tables might be the ones of a previous process, e.g. when running a kernel thread.
This can be problematic in case kernel code is being modified via text_poke() in a kernel thread, and on another processor exit_mmap() is active for the process which was running on the first cpu before the kernel thread.
As text_poke() is using a temporary address space and the former address space (obtained via cpu_tlbstate.loaded_mm) is restored afterwards, there is a race possible in case the cpu on which exit_mmap() is running wants to make sure there are no stale references to that address space on any cpu active (this e.g. is required when running as a Xen PV guest, where this problem has been observed and analyzed).
In order to avoid that, drop off TLB lazy mode before switching to the temporary address space.
Fixes: cefa929c034eb5d ("x86/mm: Introduce temporary mm structs") Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20201009144225.12019-1-jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/alternative.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index cdaab30880b91..cd6be6f143e85 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -807,6 +807,15 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) temp_mm_state_t temp_state;
lockdep_assert_irqs_disabled(); + + /* + * Make sure not to be in TLB lazy mode, as otherwise we'll end up + * with a stale address space WITHOUT being in lazy mode after + * restoring the previous mm. + */ + if (this_cpu_read(cpu_tlbstate.is_lazy)) + leave_mm(smp_processor_id()); + temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); switch_mm_irqs_off(NULL, mm, current);