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arm64: mm: Map the kernel data/bss read-only in the linear map

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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.

Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ard Biesheuvel 2026-05-29 17:02:05 +02:00 committed by Will Deacon
parent 0aae825f1e
commit f2ba877402
1 changed files with 13 additions and 2 deletions
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15
arch/arm64/mm/mmu.c
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@ -1138,7 +1138,9 @@ static void __init map_mem(void)
{ {
static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN); static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
phys_addr_t kernel_start = __pa_symbol(_text); 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(__bss_stop);
phys_addr_t start, end; phys_addr_t start, end;
int flags = NO_EXEC_MAPPINGS; int flags = NO_EXEC_MAPPINGS;
u64 i; u64 i;
@ -1173,7 +1175,11 @@ static void __init map_mem(void)
* contents of the region accessible to subsystems such as hibernate, * contents of the region accessible to subsystems such as hibernate,
* but protects it from inadvertent modification or execution. * but protects it from inadvertent modification or execution.
*/ */
__map_memblock(kernel_start, kernel_end, pgprot_tagged(PAGE_KERNEL), __map_memblock(kernel_start, init_begin, pgprot_tagged(PAGE_KERNEL),
flags);
/* Map the kernel data/bss so it can be remapped later */
__map_memblock(init_end, kernel_end, pgprot_tagged(PAGE_KERNEL),
flags); flags);
/* map all the memory banks */ /* map all the memory banks */
@ -1186,6 +1192,11 @@ static void __init map_mem(void)
__map_memblock(start, end, pgprot_tagged(PAGE_KERNEL), __map_memblock(start, end, pgprot_tagged(PAGE_KERNEL),
flags); flags);
} }
/* Map the kernel data/bss read-only in the linear map */
__map_memblock(init_end, kernel_end, PAGE_KERNEL_RO, flags);
flush_tlb_kernel_range((unsigned long)lm_alias(__init_end),
(unsigned long)lm_alias(__bss_stop));
} }
void mark_rodata_ro(void) void mark_rodata_ro(void)