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    SubjectRe: [PATCH 07/12] x86/entry/64: Always run ptregs-using syscalls on the slow path
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    On Mon, Dec 7, 2015 at 4:51 PM, Andy Lutomirski <luto@kernel.org> wrote:
    > 64-bit syscalls currently have an optimization in which they are
    > called with partial pt_regs. A small handful require full pt_regs.
    >
    > In the 32-bit and compat cases, I cleaned this up by forcing full
    > pt_regs for all syscalls. The performance hit doesn't really matter.
    >
    > I want to clean up the 64-bit case as well, but I don't want to hurt
    > fast path performance. To do that, I want to force the syscalls
    > that use pt_regs onto the slow path. This will enable us to make
    > slow path syscalls be real ABI-compliant C functions.
    >
    > Use the new syscall entry qualification machinery for this.
    > stub_clone is now stub_clone/ptregs.
    >
    > The next patch will eliminate the stubs, and we'll just have
    > sys_clone/ptregs.
    >
    > Signed-off-by: Andy Lutomirski <luto@kernel.org>

    Fails to boot, bisected to this patch:
    [ 32.675319] kernel BUG at kernel/auditsc.c:1504!
    [ 32.675325] invalid opcode: 0000 [#65] SMP
    [ 32.675328] Modules linked in:
    [ 32.675333] CPU: 1 PID: 216 Comm: systemd-cgroups Tainted: G D
    4.3.0-rc4+ #7
    [ 32.675336] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
    [ 32.675339] task: ffff880000075340 ti: ffff880036520000 task.ti:
    ffff880036520000
    [ 32.675350] RIP: 0010:[<ffffffff8113d9ed>] [<ffffffff8113d9ed>]
    __audit_syscall_entry+0xcd/0xf0
    [ 32.675353] RSP: 0018:ffff880036523ef0 EFLAGS: 00010202
    [ 32.675355] RAX: 000000000000000c RBX: ffff8800797b3000 RCX: 00007ffef8504e88
    [ 32.675357] RDX: 000056172f37cfd0 RSI: 0000000000000000 RDI: 000000000000000c
    [ 32.675359] RBP: ffff880036523f00 R08: 0000000000000001 R09: ffff880000075340
    [ 32.675361] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
    [ 32.675363] R13: 00000000c000003e R14: 0000000000000001 R15: 0000000000001000
    [ 32.675380] FS: 00007f02b4ff48c0(0000) GS:ffff88007fc80000(0000)
    knlGS:0000000000000000
    [ 32.675383] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    [ 32.675385] CR2: 00007f93d47ea0e0 CR3: 0000000036aa9000 CR4: 00000000000006e0
    [ 32.675391] Stack:
    [ 32.675396] ffff880036523f58 0000000000000000 ffff880036523f10
    ffffffff8100321b
    [ 32.675401] ffff880036523f48 ffffffff81003ad0 000056172f374040
    00007f93d45c9990
    [ 32.675404] 0000000000000001 0000000000000001 0000000000001000
    000000000000000a
    [ 32.675405] Call Trace:
    [ 32.675414] [<ffffffff8100321b>] do_audit_syscall_entry+0x4b/0x70
    [ 32.675420] [<ffffffff81003ad0>] syscall_trace_enter_phase2+0x110/0x1d0
    [ 32.675425] [<ffffffff81761d94>] tracesys+0x3a/0x96
    [ 32.675464] Code: 00 00 00 00 e8 a5 e0 fc ff c7 43 04 01 00 00 00
    48 89 43 18 48 89 53 20 44 89 63 0c c7 83 94 02 00 00 00 00 00 00 5b
    41 5c 5d c3 <0f> 0b 48 c7 43 50 00 00 00 00 48 c7 c2 60 b4 c5 81 48 89
    de 4c
    [ 32.675469] RIP [<ffffffff8113d9ed>] __audit_syscall_entry+0xcd/0xf0
    [ 32.675471] RSP <ffff880036523ef0>

    --
    Brian Gerst


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