On Fri, Oct 20, 2017 at 1:26 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Thomas Garnier <thgarnie@xxxxxxxxxx> wrote: > >> Change the assembly code to use only relative references of symbols for the >> kernel to be PIE compatible. >> >> Position Independent Executable (PIE) support will allow to extended the >> KASLR randomization range below the -2G memory limit. >> >> Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx> >> --- >> arch/x86/entry/entry_64.S | 22 +++++++++++++++------- >> 1 file changed, 15 insertions(+), 7 deletions(-) >> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index 49167258d587..15bd5530d2ae 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -194,12 +194,15 @@ entry_SYSCALL_64_fastpath: >> ja 1f /* return -ENOSYS (already in pt_regs->ax) */ >> movq %r10, %rcx >> >> + /* Ensures the call is position independent */ >> + leaq sys_call_table(%rip), %r11 >> + >> /* >> * This call instruction is handled specially in stub_ptregs_64. >> * It might end up jumping to the slow path. If it jumps, RAX >> * and all argument registers are clobbered. >> */ >> - call *sys_call_table(, %rax, 8) >> + call *(%r11, %rax, 8) >> .Lentry_SYSCALL_64_after_fastpath_call: >> >> movq %rax, RAX(%rsp) >> @@ -334,7 +337,8 @@ ENTRY(stub_ptregs_64) >> * RAX stores a pointer to the C function implementing the syscall. >> * IRQs are on. >> */ >> - cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp) >> + leaq .Lentry_SYSCALL_64_after_fastpath_call(%rip), %r11 >> + cmpq %r11, (%rsp) >> jne 1f >> >> /* >> @@ -1172,7 +1176,8 @@ ENTRY(error_entry) >> movl %ecx, %eax /* zero extend */ >> cmpq %rax, RIP+8(%rsp) >> je .Lbstep_iret >> - cmpq $.Lgs_change, RIP+8(%rsp) >> + leaq .Lgs_change(%rip), %rcx >> + cmpq %rcx, RIP+8(%rsp) >> jne .Lerror_entry_done >> >> /* >> @@ -1383,10 +1388,10 @@ ENTRY(nmi) >> * resume the outer NMI. >> */ >> >> - movq $repeat_nmi, %rdx >> + leaq repeat_nmi(%rip), %rdx >> cmpq 8(%rsp), %rdx >> ja 1f >> - movq $end_repeat_nmi, %rdx >> + leaq end_repeat_nmi(%rip), %rdx >> cmpq 8(%rsp), %rdx >> ja nested_nmi_out >> 1: >> @@ -1440,7 +1445,8 @@ nested_nmi: >> pushq %rdx >> pushfq >> pushq $__KERNEL_CS >> - pushq $repeat_nmi >> + leaq repeat_nmi(%rip), %rdx >> + pushq %rdx >> >> /* Put stack back */ >> addq $(6*8), %rsp >> @@ -1479,7 +1485,9 @@ first_nmi: >> addq $8, (%rsp) /* Fix up RSP */ >> pushfq /* RFLAGS */ >> pushq $__KERNEL_CS /* CS */ >> - pushq $1f /* RIP */ >> + pushq %rax /* Support Position Independent Code */ >> + leaq 1f(%rip), %rax /* RIP */ >> + xchgq %rax, (%rsp) /* Restore RAX, put 1f */ >> INTERRUPT_RETURN /* continues at repeat_nmi below */ >> UNWIND_HINT_IRET_REGS > > This patch seems to add extra overhead to the syscall fast-path even when PIE is > disabled, right? It does add extra instructions when one is not possible, I preferred that over ifdefing but I can change it. > > Thanks, > > Ingo -- Thomas _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
