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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2025 10:37:34.1710 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 281d1e93-4afa-4d70-c108-08dd8c8a0326 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB1PEPF0003922E.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB8347 Hi Ryan, > On 06/05/2025 11:17, Catalin Marinas wrote: > > On Tue, May 06, 2025 at 11:41:05AM +0200, Ard Biesheuvel wrote: > >> On Tue, 6 May 2025 at 10:16, Ryan Roberts wrote: > >>> On 06/05/2025 09:09, Yeoreum Yun wrote: > >>>>> On Sat, May 03, 2025 at 09:23:27PM +0100, Yeoreum Yun wrote: > >>>>>>> On Sat, May 03, 2025 at 11:16:12AM +0100, Catalin Marinas wrote: > >>>>>>>> On Fri, 02 May 2025 19:04:12 +0100, Yeoreum Yun wrote: > >>>>>>>>> create_init_idmap() could be called before .bss section initialization > >>>>>>>>> which is done in early_map_kernel(). > >>>>>>>>> Therefore, data/test_prot could be set incorrectly by PTE_MAYBE_NG macro. > >>>>>>>>> > >>>>>>>>> PTE_MAYBE_NG macro set NG bit according to value of "arm64_use_ng_mappings". > >>>>>>>>> and this variable places in .bss section. > >>>>>>>>> > >>>>>>>>> [...] > >>>>>>>> > >>>>>>>> Applied to arm64 (for-next/fixes), with some slight tweaking of the > >>>>>>>> comment, thanks! > >>>>>>>> > >>>>>>>> [1/1] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation > >>>>>>>> https://git.kernel.org/arm64/c/12657bcd1835 > >>>>>>> > >>>>>>> I'm going to drop this for now. The kernel compiled with a clang 19.1.5 > >>>>>>> version I have around (Debian sid) fails to boot, gets stuck early on: > >>>>>>> > >>>>>>> $ clang --version > >>>>>>> Debian clang version 19.1.5 (1) > >>>>>>> Target: aarch64-unknown-linux-gnu > >>>>>>> Thread model: posix > >>>>>>> InstalledDir: /usr/lib/llvm-19/bin > >>>>>>> > >>>>>>> I didn't have time to investigate, disassemble etc. I'll have a look > >>>>>>> next week. > >>>>>> > >>>>>> Just for your information. > >>>>>> When I see the debian package, clang 19.1.5-1 doesn't supply anymore: > >>>>>> - https://ftp.debian.org/debian/pool/main/l/llvm-toolchain-19/ > >>>>>> > >>>>>> and the default version for sid is below: > >>>>>> > >>>>>> $ clang-19 --version > >>>>>> Debian clang version 19.1.7 (3) > >>>>>> Target: aarch64-unknown-linux-gnu > >>>>>> Thread model: posix > >>>>>> InstalledDir: /usr/lib/llvm-19/bin > >>>>>> > >>>>>> When I tested with above version with arm64-linux's for-next/fixes > >>>>>> including this patch. it works well. > >>>>> > >>>>> It doesn't seem to be toolchain related. It fails with gcc as well from > >>>>> Debian stable but you'd need some older CPU (even if emulated, e.g. > >>>>> qemu). It fails with Cortex-A72 (guest on Raspberry Pi 4) but not > >>>>> Neoverse-N2. Also changing the annotation from __ro_after_init to > >>>>> __read_mostly also works. > >>> > >>> I think this is likely because __ro_after_init is also "ro before init" - i.e. > >>> if you try to write to it in the PI code an exception is generated due to it > >>> being mapped RO. Looks like early_map_kernel() is writiing to it. > >> > >> Indeed. > >> > >>> I've noticed a similar problem in the past and it would be nice to fix it so > >>> that PI code maps __ro_after_init RW. > >> > >> The issue is that the store occurs via the ID map, which only consists > >> of one R-X and one RW- section. I'm not convinced that it's worth the > >> hassle to relax this. > >> > >> If moving the variable to .data works, then let's just do that. > > > > Good to know there's no other more serious issue. I'll move this > > variable to __read_mostly. > > > > It seems to fail in early_map_kernel() if RANDOMIZE_BASE is enabled. > > Ahh that explains why Yeoreum Yun can't see the issue: > > if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) { > u64 kaslr_seed = kaslr_early_init(fdt, chosen); > > if (kaslr_seed && kaslr_requires_kpti()) > arm64_use_ng_mappings = true; > > kaslr_offset |= kaslr_seed & ~(MIN_KIMG_ALIGN - 1); > } Thanks to clarify me to know. I've misread the address of arm64_use_ng_mapping :( so my brain works wrong. Thanks again! -- Sincerely, Yeoreum Yun