On Tue, May 06, 2025 at 11:12:50AM +0100, Catalin Marinas wrote:
On Tue, May 06, 2025 at 09:53:57AM +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:
[...]
Personally, I don't believe this because the create_init_idmap() maps the the .rodata section with PAGE_KERNEL pgprot from __initdata_begin to _end.
and at the mark_readonly() the pgprot is changed to PAGE_KERNEL_RO But, arm64_use_ng_mappings is accessed with write before mark_readonly() only via smp_cpus_done().
JFYI here is map information:
// mark_readlonly() changes to ro perm below ranges: ffff800081b30000 g .rodata 0000000000000000 __start_rodata ffff800082560000 g .rodata.text 0000000000000000 __init_begin
// create_init_idmap() maps below range with PAGE_KERNEL. ffff8000826d0000 g .altinstructions 0000000000000000 __initdata_begin ffff800082eb0000 g .bss 0000000000000000 _end
ffff8000824596d0 g O .rodata 0000000000000001 arm64_use_ng_mappings
So arm64_use_ng_mappings is mapped as read-only since .rodata is before __initdata_begin.
Right. I've misread teh address at first time. Sorry to make noise.
-- Catalin
-- Sincerely, Yeoreum Yun