[PATCH] Arm: mm: ftrace: Only set text back to ro after kernel has been marked ro

On Tue, Dec 05, 2017 at 12:14:46PM -0800, Kees Cook wrote:

On Tue, Dec 5, 2017 at 12:09 PM, Russell King - ARM Linux
[off-list ref] wrote:

quoted

On Tue, Dec 05, 2017 at 11:35:59AM -0800, Kees Cook wrote:

quoted

We don't _need_ to, but they're all contiguous, so the ro_perms array
used by set_kernel_text_*() is actually only a single entry:

static struct section_perm ro_perms[] = {
        /* Make kernel code and rodata RX (set RO). */
        {
                .name   = "text/rodata RO",
                .start  = (unsigned long)_stext,
                .end    = (unsigned long)__init_begin,
...

Well, they may not be contiguous - it depends on DEBUG_ALIGN_RODATA.

Maybe I'm picking a slightly wrong word. I guess I meant adjacent. The
range _stext to __init_begin is all read-only, though there may be
padding (controlled by DEBUG_ALIGN_RODATA), to allow a split for NX
markings on rodata.

quoted

Either way, we have __start_rodata_section_aligned, which is either
the start of the read-only data section, or the start of the first
section beyond __start_rodata if DEBUG_ALIGN_RODATA is not set.

Given that __start_rodata_section_aligned will always be less than
__init_begin, is there any reason not to make the above end at
__start_rodata_section_aligned, thereby allowing more of the read-only
data (in the case of DEBUG_ALIGN_RODATA=n) or all of the read-only
data (in the case of DEBUG_ALIGN_RODATA=y) to remain write-protected?

Sure, there's no reason not to split this into two entries. It'll
require some reworking of the function calls to get it right,
obviously.

Gentle ping, arm is still oopsing when the function tracer is
enabled at boot time.

Tested on bcm2835 (RPiB+) with current mainline tree
(githash 90368a37fbbe) and bcm2835_defconfig.

arm64 seems to be fine, tested on bcm2837 (RPi3) with same tree and
arm64 defconfig plus function tracer enabled.

earlycon log on bvm2835:

[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.18.0-rc2+ (hias at camel2) (gcc version 4.9.3 (crosstool-NG crosstool-ng-1.22.0-88-g8460611)) #1 Fri Jun 29 10:55:21 CEST 2018
[    0.000000] CPU: ARMv6-compatible processor [410fb767] revision 7 (ARMv7), cr=00c5387d
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT nonaliasing instruction cache
[    0.000000] OF: fdt: Machine model: Raspberry Pi Model B Plus Rev 1.2
[    0.000000] earlycon: pl11 at MMIO32 0x20201000 (options '')
[    0.000000] bootconsole [pl11] enabled
[    0.000000] Memory policy: Data cache writeback
[    0.000000] cma: Reserved 32 MiB at 0x13c00000
[    0.000000] CPU: All CPU(s) started in SVC mode.
[    0.000000] random: get_random_bytes called from start_kernel+0x88/0x464 with crng_init=0
[    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 89408
[    0.000000] Kernel command line: bcm2708_fb.fbwidth=1280 bcm2708_fb.fbheight=1024 bcm2708_fb.fbswap=1 dma.dmachans=0x7f35 bcm2708.boardrev=0x10 bcm2708.serial=0x59ce1e57 bcm2708.uart_clock=48000000 bcm2708.disk_led_gpio=47 bcm2708.disk_led_active_low=0 smsc95xx.macaddr=B8:27:EB:CE:1E:57 vc_mem.mem_base=0x1ec00000 vc_mem.mem_size=0x20000000  root=/dev/mmcblk0p2 rw rootwait elevator=noop earlycon=pl011,mmio32,0x20201000 console=/dev/ttyAMA0,115200 ftrace=function
[    0.000000] Dentry cache hash table entries: 65536 (order: 6, 262144 bytes)
[    0.000000] Inode-cache hash table entries: 32768 (order: 5, 131072 bytes)
[    0.000000] Memory: 311736K/360448K available (7168K kernel code, 610K rwdata, 2328K rodata, 1024K init, 675K bss, 15944K reserved, 32768K cma-reserved)
[    0.000000] Virtual kernel memory layout:
[    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB)
[    0.000000]     fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
[    0.000000]     vmalloc : 0xd6800000 - 0xff800000   ( 656 MB)
[    0.000000]     lowmem  : 0xc0000000 - 0xd6000000   ( 352 MB)
[    0.000000]     modules : 0xbf000000 - 0xc0000000   (  16 MB)
[    0.000000]       .text : 0x(ptrval) - 0x(ptrval)   (8160 kB)
[    0.000000]       .init : 0x(ptrval) - 0x(ptrval)   (1024 kB)
[    0.000000]       .data : 0x(ptrval) - 0x(ptrval)   ( 611 kB)
[    0.000000]        .bss : 0x(ptrval) - 0x(ptrval)   ( 676 kB)
[    0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[    0.000000] ftrace: allocating 27246 entries in 80 pages
[    0.000000] Starting tracer 'function'
[    0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
[    0.000054] sched_clock: 32 bits at 1000kHz, resolution 1000ns, wraps every 2147483647500ns
[    0.008887] clocksource: timer: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns
[    0.018977] bcm2835: system timer (irq = 27)
[    0.028348] Console: colour dummy device 80x30
[    0.033444] Calibrating delay loop... 695.09 BogoMIPS (lpj=3475456)
[    0.100506] pid_max: default: 32768 minimum: 301
[    0.107059] Unable to handle kernel paging request at virtual address c0a07250
[    0.114665] pgd = (ptrval)
[    0.117541] [c0a07250] *pgd=00a0840e(bad)
[    0.121858] Internal error: Oops: 80d [#1] ARM
[    0.126369] Modules linked in:
[    0.129491] CPU: 0 PID: 0 Comm: swapper Not tainted 4.18.0-rc2+ #1
[    0.135755] Hardware name: BCM2835
[    0.139240] PC is at uts_ns_init+0x40/0x58
[    0.143395] LR is at   (null)
[    0.146406] pc : [<c0b0fde4>]    lr : [<00000000>]    psr: 60000053
[    0.152757] sp : c0c01f88  ip : c0c07120  fp : c0c01fa4
[    0.158054] r10: d5fff9c0  r9 : c0b59a28  r8 : c0c04040
[    0.163352] r7 : c0c04048  r6 : ffffffff  r5 : c0c98980  r4 : c0c989cc
[    0.169969] r3 : c0a07250  r2 : 00000000  r1 : c0209384  r0 : d3a1b300
[    0.176586] Flags: nZCv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment none
[    0.183906] Control: 00c5387d  Table: 00004008  DAC: 00000051
[    0.189730] Process swapper (pid: 0, stack limit = 0x(ptrval))
[    0.195645] Stack: (0xc0c01f88 to 0xc0c02000)
[    0.200072] 1f80:                   00000004 00000186 00000000 c0c98980 c0c01ff4 c0c01fa8
[    0.208369] 1fa0: c0b00ebc c0b0fdb0 ffffffff ffffffff 00000000 c0b00864 00000000 c0b59a28
[    0.216665] 1fc0: 1297841c 00000000 00000000 c0b00330 00000051 00c0387d 00000c42 15feca00
[    0.224961] 1fe0: 410fb767 00c5387d 00000000 c0c01ff8 00000000 c0b00b40 00000000 00000000
[    0.233301] [<c0b0fde4>] (uts_ns_init) from [<c0b00ebc>] (start_kernel+0x388/0x464)
[    0.241081] [<c0b00ebc>] (start_kernel) from [<00000000>] (  (null))
[    0.247541] Code: e3a03701 e59f0014 ebdbe4f1 e59f3010 (e5830000) 
[    0.253755] ---[ end trace fe6d5629dd3ec6e3 ]---
[    0.258446] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.265255] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
[    2.749496] random: fast init done

so long,

Hias