From 4612ff15888a2e3f886941f89da9d15d378b58f9 Mon Sep 17 00:00:00 2001
From: Alan Maguire <alan.maguire@oracle.com>
Date: Wed, 5 Feb 2025 17:00:59 +0000
Subject: [PATCH] bpf: Fix softlockup in arena_map_free on 64k page kernel
[ Upstream commit 517e8a7835e8cfb398a0aeb0133de50e31cae32b ]
On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y,
arena_htab tests cause a segmentation fault and soft lockup.
The same failure is not observed with 4k pages on aarch64.
It turns out arena_map_free() is calling
apply_to_existing_page_range() with the address returned by
bpf_arena_get_kern_vm_start(). If this address is not page-aligned
the code ends up calling apply_to_pte_range() with that unaligned
address causing soft lockup.
Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the
division by 2 in bpf_arena_get_kern_vm_start() returns
a page-aligned value.
Fixes: 317460317a02 ("bpf: Introduce bpf_arena.")
Reported-by: Colm Harrington <colm.harrington@oracle.com>
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/r/20250205170059.427458-1-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/arena.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index 93e48c7cad4ef..8c775a1401d3e 100644
--- a/kernel/bpf/arena.c
+++ b/kernel/bpf/arena.c
@@ -37,7 +37,7 @@
*/
/* number of bytes addressable by LDX/STX insn with 16-bit 'off' field */
-#define GUARD_SZ (1ull << sizeof_field(struct bpf_insn, off) * 8)
+#define GUARD_SZ round_up(1ull << sizeof_field(struct bpf_insn, off) * 8, PAGE_SIZE << 1)
#define KERN_VM_SZ (SZ_4G + GUARD_SZ)
struct bpf_arena {
--
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