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arm64: head: cover entire kernel image in initial ID map

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As a first step towards avoiding the need to create, tear down and
recreate the kernel virtual mapping with MMU and caches disabled, start
by expanding the ID map so it covers the page tables as well as all
executable code. This will allow us to populate the page tables with the
MMU and caches on, and call KASLR init code before setting up the
virtual mapping.

Since this ID map is only needed at boot, create it as a temporary set
of page tables, and populate the permanent ID map after enabling the MMU
and caches. While at it, switch to read-only attributes for the where
possible, as writable permissions are only needed for the initial kernel
page tables. Note that on 4k granule configurations, the permanent ID
map will now be reduced to a single page rather than a 2M block mapping.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220624150651.1358849-13-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ard Biesheuvel
2022-06-24 17:06:42 +02:00
committed by Will Deacon
parent b013c1e1c6
commit c3cee924bd
5 changed files with 76 additions and 21 deletions
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7
arch/arm64/kernel/vmlinux.lds.S
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@@ -198,8 +198,7 @@ SECTIONS
}
idmap_pg_dir = .;
. += IDMAP_DIR_SIZE;
idmap_pg_end = .;
. += PAGE_SIZE;
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
tramp_pg_dir = .;
@@ -235,6 +234,10 @@ SECTIONS
__inittext_end = .;
__initdata_begin = .;
init_idmap_pg_dir = .;
. += INIT_IDMAP_DIR_SIZE;
init_idmap_pg_end = .;
.init.data : {
INIT_DATA
INIT_SETUP(16)