From: Kees Cook <keescook@chromium.org>
Date: Tue, 28 Sep 2021 16:09:45 -0700
Subject: bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM
Patch-mainline: v5.16-rc1
Git-commit: 3d717fad5081b8e3bda76d86907fad95398cbde8
References: jsc#PED-1377
In order to keep ahead of cases in the kernel where Control Flow
Integrity (CFI) may trip over function call casts, enabling
-Wcast-function-type is helpful. To that end, BPF_CAST_CALL causes
various warnings and is one of the last places in the kernel triggering
this warning.
Most places using BPF_CAST_CALL actually just want a void * to perform
math on. It's not actually performing a call, so just use a different
helper to get the void *, by way of the new BPF_CALL_IMM() helper, which
can clean up a common copy/paste idiom as well.
This change results in no object code difference.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://github.com/KSPP/linux/issues/20
Link: https://lore.kernel.org/lkml/CAEf4Bzb46=-J5Fxc3mMZ8JQPtK1uoE0q6+g6WPz53Cvx=CBEhw@mail.gmail.com
Link: https://lore.kernel.org/bpf/20210928230946.4062144-2-keescook@chromium.org
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
include/linux/filter.h | 6 +++++-
kernel/bpf/hashtab.c | 6 +++---
kernel/bpf/verifier.c | 26 +++++++++-----------------
lib/test_bpf.c | 2 +-
4 files changed, 18 insertions(+), 22 deletions(-)
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -367,13 +367,17 @@ static inline bool insn_is_zext(const st
#define BPF_CAST_CALL(x) \
((u64 (*)(u64, u64, u64, u64, u64))(x))
+/* Convert function address to BPF immediate */
+
+#define BPF_CALL_IMM(x) ((void *)(x) - (void *)__bpf_call_base)
+
#define BPF_EMIT_CALL(FUNC) \
((struct bpf_insn) { \
.code = BPF_JMP | BPF_CALL, \
.dst_reg = 0, \
.src_reg = 0, \
.off = 0, \
- .imm = ((FUNC) - __bpf_call_base) })
+ .imm = BPF_CALL_IMM(FUNC) })
/* Raw code statement block */
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -668,7 +668,7 @@ static int htab_map_gen_lookup(struct bp
BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
(void *(*)(struct bpf_map *map, void *key))NULL));
- *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
+ *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 1);
*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
offsetof(struct htab_elem, key) +
@@ -709,7 +709,7 @@ static int htab_lru_map_gen_lookup(struc
BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
(void *(*)(struct bpf_map *map, void *key))NULL));
- *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
+ *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4);
*insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret,
offsetof(struct htab_elem, lru_node) +
@@ -2397,7 +2397,7 @@ static int htab_of_map_gen_lookup(struct
BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
(void *(*)(struct bpf_map *map, void *key))NULL));
- *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
+ *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2);
*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
offsetof(struct htab_elem, key) +
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1744,7 +1744,7 @@ static int add_kfunc_call(struct bpf_ver
desc = &tab->descs[tab->nr_descs++];
desc->func_id = func_id;
- desc->imm = BPF_CAST_CALL(addr) - __bpf_call_base;
+ desc->imm = BPF_CALL_IMM(addr);
err = btf_distill_func_proto(&env->log, btf_vmlinux,
func_proto, func_name,
&desc->func_model);
@@ -12514,8 +12514,7 @@ static int jit_subprogs(struct bpf_verif
if (!bpf_pseudo_call(insn))
continue;
subprog = insn->off;
- insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(func[subprog]->bpf_func);
}
/* we use the aux data to keep a list of the start addresses
@@ -12995,32 +12994,25 @@ static int do_misc_fixups(struct bpf_ver
patch_map_ops_generic:
switch (insn->imm) {
case BPF_FUNC_map_lookup_elem:
- insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_lookup_elem);
continue;
case BPF_FUNC_map_update_elem:
- insn->imm = BPF_CAST_CALL(ops->map_update_elem) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_update_elem);
continue;
case BPF_FUNC_map_delete_elem:
- insn->imm = BPF_CAST_CALL(ops->map_delete_elem) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_delete_elem);
continue;
case BPF_FUNC_map_push_elem:
- insn->imm = BPF_CAST_CALL(ops->map_push_elem) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_push_elem);
continue;
case BPF_FUNC_map_pop_elem:
- insn->imm = BPF_CAST_CALL(ops->map_pop_elem) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_pop_elem);
continue;
case BPF_FUNC_map_peek_elem:
- insn->imm = BPF_CAST_CALL(ops->map_peek_elem) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_peek_elem);
continue;
case BPF_FUNC_redirect_map:
- insn->imm = BPF_CAST_CALL(ops->map_redirect) -
- __bpf_call_base;
+ insn->imm = BPF_CALL_IMM(ops->map_redirect);
continue;
}
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -12439,7 +12439,7 @@ static __init int prepare_tail_call_test
err = -EFAULT;
goto out_err;
}
- *insn = BPF_EMIT_CALL(BPF_CAST_CALL(addr));
+ *insn = BPF_EMIT_CALL(addr);
if ((long)__bpf_call_base + insn->imm != addr)
*insn = BPF_JMP_A(0); /* Skip: NOP */
break;