Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753111AbdLENgV (ORCPT ); Tue, 5 Dec 2017 08:36:21 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:55276 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752464AbdLENgT (ORCPT ); Tue, 5 Dec 2017 08:36:19 -0500 Date: Tue, 5 Dec 2017 13:36:01 +0000 From: Russell King - ARM Linux To: Phil Elwell Cc: Matthias Reichl , Steven Rostedt , Kees Cook , LKML , Eric Anholt , Stefan Wahren , linux-rpi-kernel@lists.infradead.org, "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] Arm: mm: ftrace: Only set text back to ro after kernel has been marked ro Message-ID: <20171205133601.GX10595@n2100.armlinux.org.uk> References: <20170823135836.52fb44fc@gandalf.local.home> <20170823150351.606ba09f@gandalf.local.home> <20171205114709.f6aj6i426keq2cn5@camel2.lan> <20171205131416.GW10595@n2100.armlinux.org.uk> <20171205132339.behn34z6b7ci2m4j@camel2.lan> <5b9b86cf-4b62-c984-fe52-a22df8fce33c@raspberrypi.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5b9b86cf-4b62-c984-fe52-a22df8fce33c@raspberrypi.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9904 Lines: 168 On Tue, Dec 05, 2017 at 01:30:11PM +0000, Phil Elwell wrote: > On 05/12/2017 13:23, Matthias Reichl wrote: > > On Tue, Dec 05, 2017 at 01:14:17PM +0000, Russell King - ARM Linux wrote: > >> On Tue, Dec 05, 2017 at 12:47:09PM +0100, Matthias Reichl wrote: > >>> On Wed, Aug 23, 2017 at 03:03:51PM -0400, Steven Rostedt wrote: > >>>> On Wed, 23 Aug 2017 11:48:13 -0700 > >>>> Kees Cook wrote: > >>>> > >>>>>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c > >>>>>> index ad80548..fd75f38 100644 > >>>>>> --- a/arch/arm/mm/init.c > >>>>>> +++ b/arch/arm/mm/init.c > >>>>>> @@ -745,19 +745,29 @@ static int __mark_rodata_ro(void *unused) > >>>>>> return 0; > >>>>>> } > >>>>>> > >>>>>> +static int kernel_set_to_readonly; > >>>>> > >>>>> Adding a comment here might be a good idea, something like: > >>>>> > >>>>> /* Has system boot-up reached mark_rodata_ro() yet? */ > >>>> > >>>> I don't mind adding a comment, but the above is rather self explanatory > >>>> (one can easily see that it is set in mark_rodata_ro() with a simple > >>>> search). > >>>> > >>>> If a comment is to be added, something a bit more descriptive of the > >>>> functionality of the variable would be appropriate: > >>>> > >>>> /* > >>>> * Ignore modifying kernel text permissions until the kernel core calls > >>>> * make_rodata_ro() at system start up. > >>>> */ > >>>> > >>>> I can resend with the comment, or whoever takes this could add it > >>>> themselves. > >>> > >>> Gentle ping: this patch doesn't seem to have landed in upstream > >>> trees yet. Is any more work required? > >>> > >>> It would be nice to have this fix added. Just tested next-20171205 > >>> on RPi B+, it oopses when the function tracer is enabled during boot. > >>> next-20171205 plus this patch boots up fine. > >> > >> When does it oops? > > > > Rather early in the boot process: > > > > [ 0.000000] Booting Linux on physical CPU 0x0 > > [ 0.000000] Linux version 4.15.0-rc2-next-20171205 (hias@camel2) (gcc version 4.9.3 (crosstool-NG crosstool-ng-1.22.0-88-g8460611)) #3 Tue Dec 5 12:35:08 CET 2017 > > [ 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: fast init done > > [ 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: 311776K/360448K available (7168K kernel code, 561K rwdata, 2212K rodata, 1024K init, 683K bss, 15904K 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) ( 562 kB) > > [ 0.000000] .bss : 0x(ptrval) - 0x(ptrval) ( 684 kB) > > [ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 > > [ 0.000000] ftrace: allocating 25789 entries in 76 pages > > [ 0.000000] Starting tracer 'function' > > [ 0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16 > > [ 0.000052] sched_clock: 32 bits at 1000kHz, resolution 1000ns, wraps every 2147483647500ns > > [ 0.008889] clocksource: timer: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns > > [ 0.018979] bcm2835: system timer (irq = 27) > > [ 0.028070] Console: colour dummy device 80x30 > > [ 0.033154] Calibrating delay loop... 697.95 BogoMIPS (lpj=3489792) > > [ 0.090179] pid_max: default: 32768 minimum: 301 > > [ 0.097851] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes) > > [ 0.104852] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes) > > [ 0.117353] CPU: Testing write buffer coherency: ok > > [ 0.127472] Setting up static identity map for 0x100000 - 0x100054 > > [ 0.145654] devtmpfs: initialized > > [ 0.235561] VFP support v0.3: implementor 41 architecture 1 part 20 variant b rev 5 > > [ 0.245751] Unable to handle kernel paging request at virtual address c09eb214 > > [ 0.253373] pgd = 8aaa5336 > > [ 0.256250] [c09eb214] *pgd=0080840e(bad) > > [ 0.260567] Internal error: Oops: 80d [#1] ARM > > [ 0.265073] Modules linked in: > > [ 0.268188] CPU: 0 PID: 1 Comm: swapper Not tainted 4.15.0-rc2-next-20171205 #3 > > [ 0.275592] Hardware name: BCM2835 > > [ 0.279046] task: 11ad8790 task.stack: 886fda4c > > [ 0.283670] PC is at ksysfs_init+0x64/0xb0 > > [ 0.287840] LR is at internal_create_group+0x294/0x2c4 > > [ 0.293049] pc : [] lr : [] psr: 20000053 > > [ 0.299400] sp : d3a3ded0 ip : c028e908 fp : d3a3dee4 > > [ 0.304694] r10: 00000000 r9 : c0c8c500 r8 : c0c8c500 > > [ 0.309991] r7 : 00000000 r6 : c0c04048 r5 : c0c8d19c r4 : 00000000 > > [ 0.316607] r3 : 00000024 r2 : c0abf19c r1 : c09eb20c r0 : d3a81d80 > > [ 0.323224] Flags: nzCv IRQs on FIQs off Mode SVC_32 ISA ARM Segment none > > [ 0.330543] Control: 00c5387d Table: 00004008 DAC: 00000051 > > [ 0.336367] Process swapper (pid: 1, stack limit = 0xfa32e9e1) > > [ 0.342280] Stack: (0xd3a3ded0 to 0xd3a3e000) > > [ 0.346703] dec0: 00000001 c0b0a2d8 d3a3df5c d3a3dee8 > > [ 0.354999] dee0: c01027b0 c0b0a2e4 c0a280c0 00000000 d3a3df5c d3a3df00 c0138578 c0b00650 > > [ 0.363294] df00: d3a3df00 c0c0c328 00000000 c0a280d4 0000009f c0a280d4 00000001 00000001 > > [ 0.371590] df20: 000000a0 c0a27454 d5fffd21 d5fffd28 c014f4c0 4710e3ed 00000001 000000a0 > > [ 0.379886] df40: c0b5681c c0b7cb84 c0c8c500 c0c8c500 d3a3df94 d3a3df60 c0b00ef8 c01026f8 > > [ 0.388180] df60: 00000001 00000001 00000000 c0b00644 00000000 c07463a4 00000000 00000000 > > [ 0.396475] df80: 00000000 00000000 d3a3dfac d3a3df98 c07463bc c0b00df0 ffffffff 00000000 > > [ 0.404769] dfa0: 00000000 d3a3dfb0 c01010e8 c07463b0 00000000 00000000 00000000 00000000 > > [ 0.413061] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 > > [ 0.421354] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000 > > [ 0.429689] [] (ksysfs_init) from [] (do_one_initcall+0xc4/0x184) > > [ 0.437652] [] (do_one_initcall) from [] (kernel_init_freeable+0x114/0x1d4) > > [ 0.446490] [] (kernel_init_freeable) from [] (kernel_init+0x18/0x11c) > > [ 0.454887] [] (kernel_init) from [] (ret_from_fork+0x14/0x2c) > > [ 0.462559] Exception stack(0xd3a3dfb0 to 0xd3a3dff8) > > [ 0.467683] dfa0: 00000000 00000000 00000000 00000000 > > [ 0.475976] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 > > [ 0.484266] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000 > > [ 0.490982] Code: e3a00000 e89da830 e59f1048 e5950000 (e5813008) > > [ 0.497194] ---[ end trace 53d55c7b93eb8c51 ]--- > > [ 0.502064] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > > [ 0.502064] > > [ 0.511346] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > > [ 0.511346] > > > > so long, > > > > Hias > > > >> > >> Reading through this code, I'm left wondering why we switch the rodata > >> section to be writable here - if we're poking at kernel text, then > >> surely we shouldn't be the read-only data read-write? > >> > >> Should kernel_set_to_readonly also be a rodata-after-init variable? > > This was my initial explanation: > > 1. Data which is marked __ro_after_init is initially writeable. > > 2. The ro_perms data covers kernel text, read-only data and __ro_after_init data. > > 3. set_kernel_text_rw marks everything in ro_perms as writeable. > > 4. set_kernel_text_ro marks everything in ro_perms as read-only, including the __ro_after_init data. > > 5. Using the function tracing code involves code modification, resulting in calls to > __ftrace_modify_code and set_kernel_text_ro. > > 6. Therefore if function tracing is enabled before kernel_init has completed then the __ro_after_init > data is made read-only prematurely. My question still stands, but let me rephrase. Do we need set_kernel_text_*() to touch the read-only data? -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up