arm64: kaslr: Put kernel vectors address in separate data page

The literal pool entry for identifying the vectors base is the only piece
of information in the trampoline page that identifies the true location
of the kernel.

This patch moves it into a page-aligned region of the .rodata section
and maps this adjacent to the trampoline text via an additional fixmap
entry, which protects against any accidental leakage of the trampoline
contents.

Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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 8119b49..ec1e6d6 100644 (file)
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -59,6 +59,7 @@ enum fixed_addresses {
 #endif /* CONFIG_ACPI_APEI_GHES */
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+       FIX_ENTRY_TRAMP_DATA,
        FIX_ENTRY_TRAMP_TEXT,
 #define TRAMP_VALIAS           (__fix_to_virt(FIX_ENTRY_TRAMP_TEXT))
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 3eabcb1..031392e 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -1030,7 +1030,13 @@ alternative_else_nop_endif
        msr     tpidrro_el0, x30        // Restored in kernel_ventry
        .endif
        tramp_map_kernel        x30
+#ifdef CONFIG_RANDOMIZE_BASE
+       adr     x30, tramp_vectors + PAGE_SIZE
+alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
+       ldr     x30, [x30]
+#else
        ldr     x30, =vectors
+#endif
        prfm    plil1strm, [x30, #(1b - tramp_vectors)]
        msr     vbar_el1, x30
        add     x30, x30, #(1b - tramp_vectors)
@@ -1073,6 +1079,14 @@ END(tramp_exit_compat)
 
        .ltorg
        .popsection                             // .entry.tramp.text
+#ifdef CONFIG_RANDOMIZE_BASE
+       .pushsection ".rodata", "a"
+       .align PAGE_SHIFT
+       .globl  __entry_tramp_data_start
+__entry_tramp_data_start:
+       .quad   vectors
+       .popsection                             // .rodata
+#endif /* CONFIG_RANDOMIZE_BASE */
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 
 /*

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 6b4260f..ddfd3c0 100644 (file)
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -251,7 +251,10 @@ ASSERT(__idmap_text_end - (__idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,
 ASSERT(__hibernate_exit_text_end - (__hibernate_exit_text_start & ~(SZ_4K - 1))
        <= SZ_4K, "Hibernate exit text too big or misaligned")
 #endif
-
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == PAGE_SIZE,
+       "Entry trampoline text too big")
+#endif
 /*
  * If padding is applied before .head.text, virt<->phys conversions will fail.
  */

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index fe68a48..916d9ce 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -541,8 +541,16 @@ static int __init map_entry_trampoline(void)
        __create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE,
                             prot, pgd_pgtable_alloc, 0);
 
-       /* ...as well as the kernel page table */
+       /* Map both the text and data into the kernel page table */
        __set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot);
+       if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+               extern char __entry_tramp_data_start[];
+
+               __set_fixmap(FIX_ENTRY_TRAMP_DATA,
+                            __pa_symbol(__entry_tramp_data_start),
+                            PAGE_KERNEL_RO);
+       }
+
        return 0;
 }
 core_initcall(map_entry_trampoline);