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: 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>

diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index 4052ec39e8dbb06feb74e1161dcf26ac94744fb2..8119b49be98dc2edb27b17a1e1b4db842e79f03e 100644 (file)
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -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,
 
        /*

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 149d05fb9421520bd659b62627941ed36ce46bb3..774003b247ad06431da83c5e6bd0d1360b87eb16 100644 (file)
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -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:

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 71bf088f1e4b2e63062fd1e75320b69c0951b050..af247d10252f5019e8b44361bb4a8a724300d7e1 100644 (file)
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -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;
 }

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 267d2b79d52d6e3918a18a2c590d797bdec6d3cb..fe68a48c64cbe489f0ccdc11f7901c18fdaf6b5b 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -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.
  */