6.12-stable review patch. If anyone has any objections, please let me know.
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From: Yeoreum Yun yeoreum.yun@arm.com
commit 363cd2b81cfdf706bbfc9ec78db000c9b1ecc552 upstream.
The PTE_MAYBE_NG macro sets the nG page table bit according to the value of "arm64_use_ng_mappings". This variable is currently placed in the .bss section. create_init_idmap() is called before the .bss section initialisation which is done in early_map_kernel(). Therefore, data/test_prot in create_init_idmap() could be set incorrectly through the PAGE_KERNEL -> PROT_DEFAULT -> PTE_MAYBE_NG macros.
# llvm-objdump-21 --syms vmlinux-gcc | grep arm64_use_ng_mappings ffff800082f242a8 g O .bss 0000000000000001 arm64_use_ng_mappings
The create_init_idmap() function disassembly compiled with llvm-21:
// create_init_idmap() ffff80008255c058: d10103ff sub sp, sp, #0x40 ffff80008255c05c: a9017bfd stp x29, x30, [sp, #0x10] ffff80008255c060: a90257f6 stp x22, x21, [sp, #0x20] ffff80008255c064: a9034ff4 stp x20, x19, [sp, #0x30] ffff80008255c068: 910043fd add x29, sp, #0x10 ffff80008255c06c: 90003fc8 adrp x8, 0xffff800082d54000 ffff80008255c070: d280e06a mov x10, #0x703 // =1795 ffff80008255c074: 91400409 add x9, x0, #0x1, lsl #12 // =0x1000 ffff80008255c078: 394a4108 ldrb w8, [x8, #0x290] ------------- (1) ffff80008255c07c: f2e00d0a movk x10, #0x68, lsl #48 ffff80008255c080: f90007e9 str x9, [sp, #0x8] ffff80008255c084: aa0103f3 mov x19, x1 ffff80008255c088: aa0003f4 mov x20, x0 ffff80008255c08c: 14000000 b 0xffff80008255c08c <__pi_create_init_idmap+0x34> ffff80008255c090: aa082d56 orr x22, x10, x8, lsl #11 -------- (2)
Note (1) is loading the arm64_use_ng_mappings value in w8 and (2) is set the text or data prot with the w8 value to set PTE_NG bit. If the .bss section isn't initialized, x8 could include a garbage value and generate an incorrect mapping.
Annotate arm64_use_ng_mappings as __read_mostly so that it is placed in the .data section.
Fixes: 84b04d3e6bdb ("arm64: kernel: Create initial ID map from C code") Cc: stable@vger.kernel.org # 6.9.x Tested-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Yeoreum Yun yeoreum.yun@arm.com Link: https://lore.kernel.org/r/20250502180412.3774883-1-yeoreum.yun@arm.com [catalin.marinas@arm.com: use __read_mostly instead of __ro_after_init] [catalin.marinas@arm.com: slight tweaking of the code comment] Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/cpufeature.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
--- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -111,7 +111,14 @@ static struct arm64_cpu_capabilities con
DECLARE_BITMAP(boot_cpucaps, ARM64_NCAPS);
-bool arm64_use_ng_mappings = false; +/* + * arm64_use_ng_mappings must be placed in the .data section, otherwise it + * ends up in the .bss section where it is initialized in early_map_kernel() + * after the MMU (with the idmap) was enabled. create_init_idmap() - which + * runs before early_map_kernel() and reads the variable via PTE_MAYBE_NG - + * may end up generating an incorrect idmap page table attributes. + */ +bool arm64_use_ng_mappings __read_mostly = false; EXPORT_SYMBOL(arm64_use_ng_mappings);
DEFINE_PER_CPU_READ_MOSTLY(const char *, this_cpu_vector) = vectors;