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SubjectRe: general protection fault in perf_misc_flags
Hi,

one more thing I just spotted. The default install of syzkaller here
runs the guest with this on the kernel command line:

2020/09/30 17:56:18 running command: qemu-system-x86_64 []string{"-m", "2048",
"-smp", "2", "-display", ... "-append", "earlyprintk=serial oops=panic ...
nmi_watchdog=panic panic_on_warn=1 panic=1 ftrace_dump_on_oops=orig_cpu rodata=n
^^^^^^^^^^

which basically leaves guest kernel's memory RW and it gets caught
immediately on vm boot by CONFIG_DEBUG_WX.

This pretty much explains why kernel text can get corrupted with a stray
pointer write or so. So what's the use case for rodata=n?

[ 2.478136] Kernel memory protection disabled.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[ 2.478689] x86/mm: Checking user space page tables
[ 2.550163] ------------[ cut here ]------------
[ 2.550736] x86/mm: Found insecure W+X mapping at address entry_SYSCALL_64+0x0/0x29
[ 2.551612] WARNING: CPU: 1 PID: 1 at arch/x86/mm/dump_pagetables.c:246 note_page+0x81f/0x13a0
[ 2.552577] Kernel panic - not syncing: panic_on_warn set ...
[ 2.553240] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.9.0-rc7+ #5
[ 2.553953] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1 04/01/2014
[ 2.554922] Call Trace:
[ 2.555233] dump_stack+0x9c/0xcf
[ 2.555633] panic+0x250/0x5a0
[ 2.556004] ? __warn_printk+0xf8/0xf8
[ 2.556450] ? console_trylock+0xb0/0xb0
[ 2.556914] ? __warn.cold+0x5/0x44
[ 2.557332] ? note_page+0x81f/0x13a0
[ 2.557768] __warn.cold+0x20/0x44
[ 2.558176] ? note_page+0x81f/0x13a0
[ 2.558641] report_bug+0x168/0x1b0
[ 2.559059] handle_bug+0x3c/0x60
[ 2.559458] exc_invalid_op+0x14/0x40
[ 2.559894] asm_exc_invalid_op+0x12/0x20
[ 2.560368] RIP: 0010:note_page+0x81f/0x13a0
[ 2.560870] Code: 26 00 80 3d 9a d0 7f 02 00 0f 85 82 f9 ff ff e8 47 3c 26 00 4c 89 e6 48 c7 c7 40 aff
[ 2.562951] RSP: 0000:ffff88800e9f7a90 EFLAGS: 00010282
[ 2.563554] RAX: 0000000000000000 RBX: ffff88800e9f7e00 RCX: 0000000000000000
[ 2.564361] RDX: ffff88800e9edb80 RSI: 0000000000000004 RDI: ffffed1001d3ef44
[ 2.565167] RBP: 0000000000000200 R08: 0000000000000001 R09: 0000000000000003
[ 2.565973] R10: ffffed1001d3eefd R11: 0000000000000001 R12: ffffffff96e00000
[ 2.566780] R13: 00000000000001e3 R14: 0000000000000000 R15: ffff88800e9f7e58
[ 2.567587] ? __kprobes_text_end+0xb3598/0xb3598
[ 2.568122] ? __entry_text_end+0x1fea85/0x1fea85
[ 2.568754] ? __entry_text_end+0x1fea85/0x1fea85
[ 2.569288] ? __entry_text_end+0x1fea85/0x1fea85
[ 2.569821] ptdump_hole+0x61/0x90
[ 2.570212] ? ptdump_pte_entry+0x100/0x100
[ 2.570712] walk_pgd_range+0xdb8/0x15f0
[ 2.571178] walk_page_range_novma+0xd9/0x140
[ 2.571689] ? walk_page_range+0x2b0/0x2b0
[ 2.572171] ? console_unlock+0x58f/0xb10
[ 2.572644] ptdump_walk_pgd+0xcd/0x180
[ 2.573099] ptdump_walk_pgd_level_core+0x13c/0x1b0
[ 2.573663] ? effective_prot+0xb0/0xb0
[ 2.574117] ? vprintk_emit+0x214/0x380
[ 2.574601] ? ptdump_walk_pgd_level_core+0x1b0/0x1b0
[ 2.575186] ? memtype_copy_nth_element+0x1a0/0x1a0
[ 2.575752] ? __kprobes_text_end+0xb3598/0xb3598
[ 2.576300] ? pti_user_pagetable_walk_pmd+0x130/0x460
[ 2.576894] ? __kprobes_text_end+0xb3598/0xb3598
[ 2.577441] ? __kprobes_text_end+0xb3598/0xb3598
[ 2.577988] ? __kprobes_text_end+0xb3598/0xb3598
[ 2.578564] ? rest_init+0xdd/0xdd
[ 2.578972] ptdump_walk_user_pgd_level_checkwx.cold+0x31/0x36
[ 2.579640] pti_finalize+0x7b/0x170
[ 2.580066] kernel_init+0x5b/0x183
[ 2.580484] ret_from_fork+0x22/0x30
[ 2.581010] Dumping ftrace buffer:
[ 2.581456] (ftrace buffer empty)
ffffffffbfffffff)
[ 2.583137] Rebooting in 1 seconds..
2020/09/30 17:56:23 failed to create instance: failed to read from qemu: EOF

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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