On 02.12.20 13:32, Borislav Petkov wrote:
On Fri, Nov 20, 2020 at 12:46:22PM +0100, Juergen Gross wrote:@@ -123,12 +115,15 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL) * Try to use SYSRET instead of IRET if we're returning to * a completely clean 64-bit userspace context. If we're not, * go to the slow exit path. + * In the Xen PV case we must use iret anyway. */ - movq RCX(%rsp), %rcx - movq RIP(%rsp), %r11- cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */- jne swapgs_restore_regs_and_return_to_usermode + ALTERNATIVE __stringify( \ + movq RCX(%rsp), %rcx; \ + movq RIP(%rsp), %r11; \ + cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \ + jne swapgs_restore_regs_and_return_to_usermode), \ + "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPVWhy such a big ALTERNATIVE when you can simply do: /* * Try to use SYSRET instead of IRET if we're returning to * a completely clean 64-bit userspace context. If we're not, * go to the slow exit path. * In the Xen PV case we must use iret anyway. */ ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV movq RCX(%rsp), %rcx; movq RIP(%rsp), %r11; cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \ jne swapgs_restore_regs_and_return_to_usermode ?
I wanted to avoid the additional NOPs for the bare metal case. If you don't mind them I can do as you are suggesting. Juergen
Attachment:
OpenPGP_0xB0DE9DD628BF132F.asc
Description: application/pgp-keys
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature
_______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
