[PATCH v2 4/4] arm64: kaslr: support randomized module area with KASAN_VMALLOC

[Lecopzer Chen]

After KASAN_VMALLOC works in arm64, we can randomize module region
into vmalloc area now.

Test:
        VMALLOC area ffffffc010000000 fffffffdf0000000

        before the patch:
                module_alloc_base/end ffffffc008b80000 ffffffc010000000
        after the patch:
                module_alloc_base/end ffffffdcf4bed000 ffffffc010000000

        And the function that insmod some modules is fine.

Suggested-by: Ard Biesheuvel <a...@kernel.org>
Signed-off-by: Lecopzer Chen <lecopzer.c...@mediatek.com>
---
 arch/arm64/kernel/kaslr.c  | 18 ++++++++++--------
 arch/arm64/kernel/module.c | 16 +++++++++-------
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 1c74c45b9494..a2858058e724 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -161,15 +161,17 @@ u64 __init kaslr_early_init(u64 dt_phys)
        /* use the top 16 bits to randomize the linear region */
        memstart_offset_seed = seed >> 48;
 
-       if (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
-           IS_ENABLED(CONFIG_KASAN_SW_TAGS))
+       if (!IS_ENABLED(CONFIG_KASAN_VMALLOC) &&
+           (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
+            IS_ENABLED(CONFIG_KASAN_SW_TAGS)))
                /*
-                * KASAN does not expect the module region to intersect the
-                * vmalloc region, since shadow memory is allocated for each
-                * module at load time, whereas the vmalloc region is shadowed
-                * by KASAN zero pages. So keep modules out of the vmalloc
-                * region if KASAN is enabled, and put the kernel well within
-                * 4 GB of the module region.
+                * KASAN without KASAN_VMALLOC does not expect the module region
+                * to intersect the vmalloc region, since shadow memory is
+                * allocated for each module at load time, whereas the vmalloc
+                * region is shadowed by KASAN zero pages. So keep modules
+                * out of the vmalloc region if KASAN is enabled without
+                * KASAN_VMALLOC, and put the kernel well within 4 GB of the
+                * module region.
                 */
                return offset % SZ_2G;
 
diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index fe21e0f06492..b5ec010c481f 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -40,14 +40,16 @@ void *module_alloc(unsigned long size)
                                NUMA_NO_NODE, __builtin_return_address(0));
 
        if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
-           !IS_ENABLED(CONFIG_KASAN_GENERIC) &&
-           !IS_ENABLED(CONFIG_KASAN_SW_TAGS))
+           (IS_ENABLED(CONFIG_KASAN_VMALLOC) ||
+            (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+             !IS_ENABLED(CONFIG_KASAN_SW_TAGS))))
                /*
-                * KASAN can only deal with module allocations being served
-                * from the reserved module region, since the remainder of
-                * the vmalloc region is already backed by zero shadow pages,
-                * and punching holes into it is non-trivial. Since the module
-                * region is not randomized when KASAN is enabled, it is even
+                * KASAN without KASAN_VMALLOC can only deal with module
+                * allocations being served from the reserved module region,
+                * since the remainder of the vmalloc region is already
+                * backed by zero shadow pages, and punching holes into it
+                * is non-trivial. Since the module region is not randomized
+                * when KASAN is enabled without KASAN_VMALLOC, it is even
                 * less likely that the module region gets exhausted, so we
                 * can simply omit this fallback in that case.
                 */
-- 
2.25.1