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FROMLIST: arm64: mm: Map entry trampoline into trampoline and kernel page tables

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The exception entry trampoline needs to be mapped at the same virtual
address in both the trampoline page table (which maps nothing else)
and also the kernel page table, so that we can swizzle TTBR1_EL1 on
exceptions from and return to EL0.

This patch maps the trampoline at a fixed virtual address in the fixmap
area of the kernel virtual address space, which allows the kernel proper
to be randomized with respect to the trampoline when KASLR is enabled.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
 commit 51a0048beb449682d632d0af52a515adb9f9882e)

Change-Id: I31b2dcdf4db36c3e31181fe43ccb984f9efb6ac6
[ghackmann@google.com:
 - adjust context
 - tweak __create_pgd_mapping() call to match 4.4 APIs]
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Will Deacon 2017-11-14 14:14:17 +00:00 • committed by Greg Kroah-Hartman
parent 6fdb633b0b
commit 39685f556c
4 changed files with 33 additions and 0 deletions
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4
arch/arm64/include/asm/fixmap.h
View file

@ -50,6 +50,10 @@ enum fixed_addresses {
FIX_EARLYCON_MEM_BASE,
FIX_TEXT_POKE0,
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
FIX_ENTRY_TRAMP_TEXT,
#define TRAMP_VALIAS (__fix_to_virt(FIX_ENTRY_TRAMP_TEXT))
#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
__end_of_permanent_fixed_addresses,
/*

1
arch/arm64/include/asm/pgtable.h
View file

@ -714,6 +714,7 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
extern pgd_t tramp_pg_dir[PTRS_PER_PGD];
/*
* Encode and decode a swap entry:

5
arch/arm64/kernel/asm-offsets.c
View file

@ -22,6 +22,7 @@
#include <linux/mm.h>
#include <linux/dma-mapping.h>
#include <linux/kvm_host.h>
#include <asm/fixmap.h>
#include <asm/thread_info.h>
#include <asm/memory.h>
#include <asm/smp_plat.h>
@ -182,5 +183,9 @@ int main(void)
#endif
DEFINE(ARM_SMCCC_RES_X0_OFFS, offsetof(struct arm_smccc_res, a0));
DEFINE(ARM_SMCCC_RES_X2_OFFS, offsetof(struct arm_smccc_res, a2));
BLANK();
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
DEFINE(TRAMP_VALIAS, TRAMP_VALIAS);
#endif
return 0;
}

23
arch/arm64/mm/mmu.c
View file

@ -494,6 +494,29 @@ static void __init map_kernel_chunk(pgd_t *pgd, void *va_start, void *va_end,
vm_area_add_early(vma);
}
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
static int __init map_entry_trampoline(void)
{
extern char __entry_tramp_text_start[];
pgprot_t prot = PAGE_KERNEL_EXEC;
phys_addr_t pa_start = __pa_symbol(__entry_tramp_text_start);
/* The trampoline is always mapped and can therefore be global */
pgprot_val(prot) &= ~PTE_NG;
/* Map only the text into the trampoline page table */
memset(tramp_pg_dir, 0, PGD_SIZE);
__create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE,
prot, late_pgtable_alloc);
/* ...as well as the kernel page table */
__set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot);
return 0;
}
core_initcall(map_entry_trampoline);
#endif
/*
* Create fine-grained mappings for the kernel.
*/