Commit 51a0048b authored by Will Deacon's avatar Will Deacon
Browse files

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



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: default avatarMark Rutland <mark.rutland@arm.com>
Tested-by: default avatarLaura Abbott <labbott@redhat.com>
Tested-by: default avatarShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent c7b9adaf

arch/arm64/include/asm/fixmap.h

+4 −0
Original line number Diff line number Diff line
@@ -58,6 +58,10 @@ enum fixed_addresses { 
	FIX_APEI_GHES_NMI,

#endif /* CONFIG_ACPI_APEI_GHES */



#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,



	/*

arch/arm64/include/asm/pgtable.h

+1 −0
Original line number Diff line number Diff line
@@ -680,6 +680,7 @@ 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:

arch/arm64/kernel/asm-offsets.c

+5 −1
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 
#include <linux/kvm_host.h>

#include <linux/suspend.h>

#include <asm/cpufeature.h>

#include <asm/fixmap.h>

#include <asm/thread_info.h>

#include <asm/memory.h>

#include <asm/smp_plat.h>
@@ -148,11 +149,14 @@ int main(void) 
  DEFINE(ARM_SMCCC_RES_X2_OFFS,		offsetof(struct arm_smccc_res, a2));

  DEFINE(ARM_SMCCC_QUIRK_ID_OFFS,	offsetof(struct arm_smccc_quirk, id));

  DEFINE(ARM_SMCCC_QUIRK_STATE_OFFS,	offsetof(struct arm_smccc_quirk, state));



  BLANK();

  DEFINE(HIBERN_PBE_ORIG,	offsetof(struct pbe, orig_address));

  DEFINE(HIBERN_PBE_ADDR,	offsetof(struct pbe, address));

  DEFINE(HIBERN_PBE_NEXT,	offsetof(struct pbe, next));

  DEFINE(ARM64_FTR_SYSVAL,	offsetof(struct arm64_ftr_reg, sys_val));

  BLANK();

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

  DEFINE(TRAMP_VALIAS,		TRAMP_VALIAS);

#endif

  return 0;

}

arch/arm64/mm/mmu.c

+23 −0
Original line number Diff line number Diff line
@@ -525,6 +525,29 @@ static int __init parse_rodata(char *arg) 
}

early_param("rodata", parse_rodata);



#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

static int __init map_entry_trampoline(void)

{

	extern char __entry_tramp_text_start[];



	pgprot_t prot = rodata_enabled ? PAGE_KERNEL_ROX : 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, pgd_pgtable_alloc, 0);



	/* ...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.

 */

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