• Zhenzhong Duan's avatar
    xen/pv: Fix a boot up hang revealed by int3 self test · b23e5844
    Zhenzhong Duan authored
    Commit 7457c0da ("x86/alternatives: Add int3_emulate_call()
    selftest") is used to ensure there is a gap setup in int3 exception stack
    which could be used for inserting call return address.
    
    This gap is missed in XEN PV int3 exception entry path, then below panic
    triggered:
    
    [    0.772876] general protection fault: 0000 [#1] SMP NOPTI
    [    0.772886] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0+ #11
    [    0.772893] RIP: e030:int3_magic+0x0/0x7
    [    0.772905] RSP: 3507:ffffffff82203e98 EFLAGS: 00000246
    [    0.773334] Call Trace:
    [    0.773334]  alternative_instructions+0x3d/0x12e
    [    0.773334]  check_bugs+0x7c9/0x887
    [    0.773334]  ? __get_locked_pte+0x178/0x1f0
    [    0.773334]  start_kernel+0x4ff/0x535
    [    0.773334]  ? set_init_arg+0x55/0x55
    [    0.773334]  xen_start_kernel+0x571/0x57a
    
    For 64bit PV guests, Xen's ABI enters the kernel with using SYSRET, with
    %rcx/%r11 on the stack. To convert back to "normal" looking exceptions,
    the xen thunks do 'xen_*: pop %rcx; pop %r11; jmp *'.
    
    E.g. Extracting 'xen_pv_trap xenint3' we have:
    xen_xenint3:
     pop %rcx;
     pop %r11;
     jmp xenint3
    
    As xenint3 and int3 entry code are same except xenint3 doesn't generate
    a gap, we can fix it by using int3 and drop useless xenint3.
    Signed-off-by: default avatarZhenzhong Duan <zhenzhong.duan@oracle.com>
    Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Stefano Stabellini <sstabellini@kernel.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Andrew Cooper <andrew.cooper3@citrix.com>
    Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
    b23e5844
traps.h 6.46 KB