On Fri, Oct 20, 2023 at 01:45:03PM -0700, Pawan Gupta wrote: > @@ -663,6 +665,10 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) > /* Restore RDI. */ > popq %rdi > swapgs > + > + /* Mitigate CPU data sampling attacks .e.g. MDS */ > + USER_CLEAR_CPU_BUFFERS > + > jmp .Lnative_iret > > > @@ -774,6 +780,9 @@ native_irq_return_ldt: > */ > popq %rax /* Restore user RAX */ > > + /* Mitigate CPU data sampling attacks .e.g. MDS */ > + USER_CLEAR_CPU_BUFFERS > + Can the above two USER_CLEAR_CPU_BUFFERS be replaced with a single one just above native_irq_return_iret? Otherwise the native_irq_return_ldt case ends up getting two VERWs. > /* > * RSP now points to an ordinary IRET frame, except that the page > * is read-only and RSP[31:16] are preloaded with the userspace > @@ -1502,6 +1511,9 @@ nmi_restore: > std > movq $0, 5*8(%rsp) /* clear "NMI executing" */ > > + /* Mitigate CPU data sampling attacks .e.g. MDS */ > + USER_CLEAR_CPU_BUFFERS > + > /* > * iretq reads the "iret" frame and exits the NMI stack in a > * single instruction. We are returning to kernel mode, so this This isn't needed here. This is the NMI return-to-kernel path. The NMI return-to-user path is already mitigated as it goes through swapgs_restore_regs_and_return_to_usermode. -- Josh
