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arm64: Reduce the kernel executable pages

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When creating the kernel page tables we create them all executable to
allow the kernel to boot.

We can reduce the number of l2 blocks or l3 pages created as executable
by looking where the end of the .text section is and only marking
memory up to this as executable (rounded up to the block/page size).

Memory after the .text is marked as execute never as it will be data.

Reviewed by:	alc
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D45063
This commit is contained in:
Andrew Turner 2025-06-12 10:37:27 +01:00
parent 95059bef24
commit e6928c33f6
1 changed files with 18 additions and 1 deletions
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19
sys/arm64/arm64/locore.S
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@ -598,7 +598,14 @@ common:
#endif
/* Get the number of blocks/pages to allocate, rounded down */
lsr x10, x8, #(PTE_SHIFT)
lsr x14, x8, #(PTE_SHIFT)
ldr x25, =etext
ldr x8, =((1 << PTE_SHIFT) - 1)
add x25, x25, x8
mov x8, #(KERNBASE)
sub x25, x25, x8
lsr x25, x25, #(PTE_SHIFT)
/* Create the kernel space PTE table */
adrp x6, LL_PAGE_TABLE
@ -606,6 +613,16 @@ common:
mov x7, #(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK))
mov x8, #(KERNBASE)
mov x9, x28
mov x10, x25
bl BUILD_PTE_FUNC
/* Create the kernel space XN PTE table */
lsl x10, x25, #(PTE_SHIFT)
ldr x7, =(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK) | ATTR_S1_XN)
ldr x8, =(KERNBASE)
add x8, x8, x10
add x9, x28, x10
sub x10, x14, x25
bl BUILD_PTE_FUNC
#undef PTE_SHIFT