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    SubjectRe: general protection fault in syscall_return_slowpath
    On Sun, Mar 8, 2020 at 5:40 PM syzbot
    <syzbot+cd66e43794b178bb5cd6@syzkaller.appspotmail.com> wrote:
    > syzbot found the following crash on:
    >
    > HEAD commit: 63623fd4 Merge tag 'for-linus' of git://git.kernel.org/pub..
    > git tree: upstream
    > console output: https://syzkaller.appspot.com/x/log.txt?x=16cfeac3e00000
    > kernel config: https://syzkaller.appspot.com/x/.config?x=5d2e033af114153f
    > dashboard link: https://syzkaller.appspot.com/bug?extid=cd66e43794b178bb5cd6
    > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
    > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12a42329e00000
    [...]
    > general protection fault, probably for non-canonical address 0x1ffffffff1255a6b: 0000 [#1] PREEMPT SMP KASAN
    > CPU: 0 PID: 8742 Comm: syz-executor.2 Not tainted 5.6.0-rc3-syzkaller #0
    > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    > RIP: 0010:arch_local_irq_disable arch/x86/include/asm/paravirt.h:757 [inline]
    > RIP: 0010:syscall_return_slowpath+0xeb/0x4a0 arch/x86/entry/common.c:277
    > Code: 00 10 0f 85 de 00 00 00 e8 b2 a3 76 00 48 c7 c0 58 d3 2a 89 48 c1 e8 03 80 3c 18 00 74 0c 48 c7 c7 58 d3 2a 89 e8 05 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    > RSP: 0018:ffffc900020a7ed0 EFLAGS: 00010246
    > RAX: 1ffffffff1255a6b RBX: dffffc0000000000 RCX: ffff88808c512380
    > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
    > RBP: ffffc900020a7f10 R08: ffffffff810075bb R09: fffffbfff14d9182
    > R10: fffffbfff14d9182 R11: 0000000000000000 R12: 1ffff110118a2470
    > R13: 0000000000004000 R14: ffff88808c512380 R15: ffff88808c512380
    > FS: 000000000154f940(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
    > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > CR2: 000000000076c000 CR3: 00000000a6b05000 CR4: 00000000001406f0
    > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

    Let's see if we can get syzkaller to tell us which fbcon
    implementation it's hitting...

    #syz test: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux.git
    63623fd44972d1ed2bfb6e0fb631dfcf547fd1e7
    From 8442144fe582ab38985378cf21ca88de1594b5df Mon Sep 17 00:00:00 2001
    From: Jann Horn <jannh@google.com>
    Date: Sun, 8 Mar 2020 18:15:11 +0100
    Subject: [PATCH] FOR TESTING ONLY: tell us which fbcon implementation is used

    ---
    drivers/tty/vt/vt.c | 10 ++++++++--
    1 file changed, 8 insertions(+), 2 deletions(-)

    diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
    index 0cfbb7182b5a..b3dd44802208 100644
    --- a/drivers/tty/vt/vt.c
    +++ b/drivers/tty/vt/vt.c
    @@ -4590,7 +4590,7 @@ static int con_font_copy(struct vc_data *vc, struct console_font_op *op)
    {
    int con = op->height;
    int rc;
    -
    + static void *LAST;

    console_lock();
    if (vc->vc_mode != KD_TEXT)
    @@ -4601,8 +4601,14 @@ static int con_font_copy(struct vc_data *vc, struct console_font_op *op)
    rc = -ENOTTY;
    else if (con == vc->vc_num) /* nothing to do */
    rc = 0;
    - else
    + else {
    + if (LAST != vc->vc_sw) {
    + pr_warn("con_font_copy(): vc_sw=%pS, vc_sw->con_font_copy=%pS\n",
    + vc->vc_sw, vc->vc_sw->con_font_copy);
    + LAST = vc->vc_sw;
    + }
    rc = vc->vc_sw->con_font_copy(vc, con);
    + }
    console_unlock();
    return rc;
    }
    base-commit: 63623fd44972d1ed2bfb6e0fb631dfcf547fd1e7
    --
    2.25.1.481.gfbce0eb801-goog

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