Messages in this thread | | | From | Ard Biesheuvel <> | Date | Wed, 30 Mar 2022 19:42:31 +0200 | Subject | Re: CONFIG_THUMB2_KERNEL=y boot failure after Spectre BHB fixes |
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On Wed, 30 Mar 2022 at 19:33, Christian Eggers <ceggers@arri.de> wrote: > > On Wednesday, 30 March 2022, 18:45:18 CEST, Ard Biesheuvel wrote: > > > On Wed, 30 Mar 2022 at 18:37, Russell King (Oracle) > > <linux@armlinux.org.uk> wrote: > > > > > > On Wed, Mar 30, 2022 at 06:34:25PM +0200, Ard Biesheuvel wrote: > > > > On Wed, 30 Mar 2022 at 18:12, Russell King (Oracle) > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > On Tue, Mar 22, 2022 at 06:49:17PM +0100, Christian Eggers wrote: > > > > > > Hi Nathan, hi Russel, > > > > > > > > > > > > I stumbled today over the same problem (no output on serial console > > > > > > with v5.15.28-rt36). During `git bisect`, I had also some commits > > > > > > where a few lines of output were visible. > > > > > > > > > > > > At commit 8d9d651ff227 ("ARM: use LOADADDR() to get load address of > > > > > > sections"), the system boots up to here: > > > > > > > > > > > > start_kernel() > > > > > > +--setup_arch() > > > > > > +--paging_init() > > > > > > +--devicemaps_init() > > > > > > +--eary_trap_init(vectors_base = 0xC7FFE000) > > > > > > +--copy_from_lma(vectors_base = 0xC7FFE000, __vectors_start=0x0, __vectors_end=0x20) > > > > > > +--__memcpy() > > > > > > > > > > > > copy_template.S:113 > > > > > > ldr8w r1, r3, r4, r5, r6, r7, r8, ip, lr, abort=20f > > > > > > r1 = 0 > > > > > > > > > > > > > > > > > > With the final v5.15.28-rt36 I found out that the system boots fine > > > > > > after disabling CONFIG_HARDEN_BRANCH_HISTORY. > > > > > > > > > > > > Is there anything else I could analyze? My SoC system is a NXP i.MX6LL > > > > > > with a ARMv7 core. I have access to a JTAG debugger. > > > > > > > > > > I think this is already fixed in mainline. Commit: > > > > > > > > > > 6c7cb60bff7a ("ARM: fix Thumb2 regression") > > > > > > > > > > > > > It's still broken - I sent a couple of patches on Monday, among which > > > > one to fix the boot issue with loop8 on Thumb2. The problem is 'b . + > > > > 4', which produces a narrow encoding, and so it skips the subsequent > > > > subs instruction and loops forever. > > > > > > And what's the current status? Sorry, I've way too much email from the > > > last 2.5 weeks to find it myself. > > > > > > > https://lore.kernel.org/linux-arm-kernel/20220328134714.205342-1-ardb@kernel.org/ > > > > Nobody bothered to respond yet, I can drop the first two in the patch > > tracker if you like. > > I just switched to v5.15.31-rt38 which already includes > 6c7cb60bff7a ("ARM: fix Thumb2 regression") > > This kernel boots fine now, even with CONFIG_HARDEN_BRANCH_HISTORY=y. After > applying the patch series from Ard, the system still boots fine. > > I haven't any understanding what these patches do. Is there anything I shall > test? >
Thanks for confirming. The first fix affects all Thumb2 configurations, my patch only affects Thumb2 configurations that actually enable the loop8 mitigation for Spectre-BHB.
What type of CPU are you booting on?
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