On 26/01/2026 09:26, Ard Biesheuvel wrote: > From: Ard Biesheuvel <[email protected]> > > On systems where the bootloader adheres to the original arm64 boot > protocol, the placement of the kernel in the physical address space is > highly predictable, and this makes the placement of its linear alias in > the kernel virtual address space equally predictable, given the lack of > randomization of the linear map. > > The linear aliases of the kernel text and rodata regions are already > mapped read-only, but the kernel data and bss are mapped read-write in > this region. This is not needed, so map them read-only as well. > > Note that the statically allocated kernel page tables do need to be > modifiable via the linear map, so leave these mapped read-write. > > Signed-off-by: Ard Biesheuvel <[email protected]> > --- > arch/arm64/include/asm/sections.h | 1 + > arch/arm64/mm/mmu.c | 10 ++++++++-- > 2 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/sections.h > b/arch/arm64/include/asm/sections.h > index 51b0d594239e..f7fe2bcbfd03 100644 > --- a/arch/arm64/include/asm/sections.h > +++ b/arch/arm64/include/asm/sections.h > @@ -23,6 +23,7 @@ extern char __irqentry_text_start[], __irqentry_text_end[]; > extern char __mmuoff_data_start[], __mmuoff_data_end[]; > extern char __entry_tramp_text_start[], __entry_tramp_text_end[]; > extern char __relocate_new_kernel_start[], __relocate_new_kernel_end[]; > +extern char __pgdir_start[]; > > static inline size_t entry_tramp_text_size(void) > { > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 18415d4743bf..fdbbb018adc5 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1122,7 +1122,9 @@ static void __init map_mem(void) > { > static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN); > phys_addr_t kernel_start = __pa_symbol(_text); > - phys_addr_t kernel_end = __pa_symbol(__init_begin); > + phys_addr_t init_begin = __pa_symbol(__init_begin); > + phys_addr_t init_end = __pa_symbol(__init_end); > + phys_addr_t kernel_end = __pa_symbol(__pgdir_start); > phys_addr_t start, end; > phys_addr_t early_kfence_pool; > int flags = NO_EXEC_MAPPINGS; > @@ -1158,7 +1160,9 @@ static void __init map_mem(void) > * Note that contiguous mappings cannot be remapped in this way, > * so we should avoid them here. > */ > - __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, > + __map_memblock(kernel_start, init_begin, PAGE_KERNEL, > + flags | NO_CONT_MAPPINGS); > + __map_memblock(init_end, kernel_end, PAGE_KERNEL, > flags | NO_CONT_MAPPINGS);
I'm probably being dumb again... why map [init_end, kernel_end) RW here, only to remap RO below? Why not just map RO here? > > /* map all the memory banks */ > @@ -1172,6 +1176,8 @@ static void __init map_mem(void) > flags); > } > > + __map_memblock(init_end, kernel_end, PAGE_KERNEL_RO, > + flags | NO_CONT_MAPPINGS); This seems iffy since __map_memblock() doesn't flush the tlb. If you want to update an existing mapping you want to be calling update_mapping_prot() right? Thanks, Ryan > arm64_kfence_map_pool(early_kfence_pool); > } >
