| Message ID | 20171011203027.11248-7-thgarnie@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* Thomas Garnier <thgarnie@google.com> 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@google.com> > --- > 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? Thanks, Ingo
On Fri, Oct 20, 2017 at 1:26 AM, Ingo Molnar <mingo@kernel.org> wrote: > > * Thomas Garnier <thgarnie@google.com> 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@google.com> >> --- >> 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 Garnier <thgarnie@google.com> wrote: > >> */ > >> - cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp) > >> + leaq .Lentry_SYSCALL_64_after_fastpath_call(%rip), %r11 > >> + cmpq %r11, (%rsp) > >> jne 1f > > 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. So my problem is, this pattern repeats in many other places as well, but sprinking various pieces of assembly code with #ifdefs would be very bad as well. I have no good idea how to solve this. Thanks, Ingo
> On Oct 20, 2017, at 5:20 PM, Ingo Molnar <mingo@kernel.org> wrote: > > > * Thomas Garnier <thgarnie@google.com> wrote: > >>>> */ >>>> - cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp) >>>> + leaq .Lentry_SYSCALL_64_after_fastpath_call(%rip), %r11 >>>> + cmpq %r11, (%rsp) >>>> jne 1f > >>> 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. > > So my problem is, this pattern repeats in many other places as well, but sprinking > various pieces of assembly code with #ifdefs would be very bad as well. > > I have no good idea how to solve this. > How about: .macro JMP_TO_LABEL ... > Thanks, > > Ingo
> On Oct 20, 2017, at 5:20 PM, Ingo Molnar <mingo@kernel.org> wrote: > > > * Thomas Garnier <thgarnie@google.com> wrote: > >>>> */ >>>> - cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp) >>>> + leaq .Lentry_SYSCALL_64_after_fastpath_call(%rip), %r11 >>>> + cmpq %r11, (%rsp) >>>> jne 1f > >>> 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. > > So my problem is, this pattern repeats in many other places as well, but sprinking > various pieces of assembly code with #ifdefs would be very bad as well. > > I have no good idea how to solve this. > > Thanks, Ugh, brain was off. This is a bit messy. We could use a macro for this, too, I suppose. > > Ingo
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 1:
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@google.com> --- arch/x86/entry/entry_64.S | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-)