Commit-ID: fa2016a8e7d846b306e431646d250500e1da0c33 Gitweb: http://git.kernel.org/tip/fa2016a8e7d846b306e431646d250500e1da0c33 Author: Andy Lutomirski <[email protected]> AuthorDate: Mon, 14 Aug 2017 22:36:19 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 15 Aug 2017 10:10:58 +0200
x86/xen/64: Fix the reported SS and CS in SYSCALL When I cleaned up the Xen SYSCALL entries, I inadvertently changed the reported segment registers. Before my patch, regs->ss was __USER(32)_DS and regs->cs was __USER(32)_CS. After the patch, they are FLAT_USER_CS/DS(32). This had a couple unfortunate effects. It confused the opportunistic fast return logic. It also significantly increased the risk of triggering a nasty glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=21269 Update the Xen entry code to change it back. Reported-by: Brian Gerst <[email protected]> Signed-off-by: Andy Lutomirski <[email protected]> Cc: Andrew Cooper <[email protected]> Cc: Boris Ostrovsky <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Juergen Gross <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Fixes: 8a9949bc71a7 ("x86/xen/64: Rearrange the SYSCALL entries") Link: http://lkml.kernel.org/r/daba8351ea2764bb30272296ab9ce08a81bd8264.1502775273.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/xen/xen-asm_64.S | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S index a8a4f4c..c5fee26 100644 --- a/arch/x86/xen/xen-asm_64.S +++ b/arch/x86/xen/xen-asm_64.S @@ -88,6 +88,15 @@ RELOC(xen_sysret64, 1b+1) ENTRY(xen_syscall_target) popq %rcx popq %r11 + + /* + * Neither Xen nor the kernel really knows what the old SS and + * CS were. The kernel expects __USER_DS and __USER_CS, so + * report those values even though Xen will guess its own values. + */ + movq $__USER_DS, 4*8(%rsp) + movq $__USER_CS, 1*8(%rsp) + jmp entry_SYSCALL_64_after_hwframe ENDPROC(xen_syscall_target) @@ -97,6 +106,15 @@ ENDPROC(xen_syscall_target) ENTRY(xen_syscall32_target) popq %rcx popq %r11 + + /* + * Neither Xen nor the kernel really knows what the old SS and + * CS were. The kernel expects __USER32_DS and __USER32_CS, so + * report those values even though Xen will guess its own values. + */ + movq $__USER32_DS, 4*8(%rsp) + movq $__USER32_CS, 1*8(%rsp) + jmp entry_SYSCALL_compat_after_hwframe ENDPROC(xen_syscall32_target)
