bpf-for-netdev

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Merge tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf

Daniel Borkmann says:

====================
pull-request: bpf 2024-06-14

We've added 8 non-merge commits during the last 2 day(s) which contain
a total of 9 files changed, 92 insertions(+), 11 deletions(-).

The main changes are:

1) Silence a syzkaller splat under CONFIG_DEBUG_NET=y in pskb_pull_reason()
   triggered via __bpf_try_make_writable(), from Florian Westphal.

2) Fix removal of kfuncs during linking phase which then throws a kernel
   build warning via resolve_btfids about unresolved symbols,
   from Tony Ambardar.

3) Fix a UML x86_64 compilation failure from BPF as pcpu_hot symbol
   is not available on User Mode Linux, from Maciej Żenczykowski.

4) Fix a register corruption in reg_set_min_max triggering an invariant
   violation in BPF verifier, from Daniel Borkmann.

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
  bpf: Harden __bpf_kfunc tag against linker kfunc removal
  compiler_types.h: Define __retain for __attribute__((__retain__))
  bpf: Avoid splat in pskb_pull_reason
  bpf: fix UML x86_64 compile failure
  selftests/bpf: Add test coverage for reg_set_min_max handling
  bpf: Reduce stack consumption in check_stack_write_fixed_off
  bpf: Fix reg_set_min_max corruption of fake_reg
  MAINTAINERS: mailmap: Update Stanislav's email address
====================

Link: https://lore.kernel.org/r/20240614203223.26500-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

.mailmap

@@ -608,6 +608,7 @@ Simon Kelley <simon@thekelleys.org.uk>
 Sricharan Ramabadhran <quic_srichara@quicinc.com> <sricharan@codeaurora.org>
 Srinivas Ramana <quic_sramana@quicinc.com> <sramana@codeaurora.org>
 Sriram R <quic_srirrama@quicinc.com> <srirrama@codeaurora.org>
+Stanislav Fomichev <sdf@fomichev.me> <sdf@google.com>
 Stefan Wahren <wahrenst@gmx.net> <stefan.wahren@i2se.com>
 Stéphane Witzmann <stephane.witzmann@ubpmes.univ-bpclermont.fr>
 Stephen Hemminger <stephen@networkplumber.org> <shemminger@linux-foundation.org>

MAINTAINERS

@@ -3980,7 +3980,7 @@ R:	Song Liu <song@kernel.org>
 R:	Yonghong Song <yonghong.song@linux.dev>
 R:	John Fastabend <john.fastabend@gmail.com>
 R:	KP Singh <kpsingh@kernel.org>
-R:	Stanislav Fomichev <sdf@google.com>
+R:	Stanislav Fomichev <sdf@fomichev.me>
 R:	Hao Luo <haoluo@google.com>
 R:	Jiri Olsa <jolsa@kernel.org>
 L:	bpf@vger.kernel.org

include/linux/bpf_verifier.h

@@ -746,6 +746,8 @@ struct bpf_verifier_env {
 	/* Same as scratched_regs but for stack slots */
 	u64 scratched_stack_slots;
 	u64 prev_log_pos, prev_insn_print_pos;
+	/* buffer used to temporary hold constants as scalar registers */
+	struct bpf_reg_state fake_reg[2];
 	/* buffer used to generate temporary string representations,
 	 * e.g., in reg_type_str() to generate reg_type string
 	 */

include/linux/btf.h

@@ -82,7 +82,7 @@
  * as to avoid issues such as the compiler inlining or eliding either a static
  * kfunc, or a global kfunc in an LTO build.
  */
-#define __bpf_kfunc __used noinline
+#define __bpf_kfunc __used __retain noinline
 
 #define __bpf_kfunc_start_defs()					       \
 	__diag_push();							       \

include/linux/compiler_types.h

@@ -143,6 +143,29 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
 # define __preserve_most
 #endif
 
+/*
+ * Annotating a function/variable with __retain tells the compiler to place
+ * the object in its own section and set the flag SHF_GNU_RETAIN. This flag
+ * instructs the linker to retain the object during garbage-cleanup or LTO
+ * phases.
+ *
+ * Note that the __used macro is also used to prevent functions or data
+ * being optimized out, but operates at the compiler/IR-level and may still
+ * allow unintended removal of objects during linking.
+ *
+ * Optional: only supported since gcc >= 11, clang >= 13
+ *
+ *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-retain-function-attribute
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#retain
+ */
+#if __has_attribute(__retain__) && \
+	(defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || \
+	 defined(CONFIG_LTO_CLANG))
+# define __retain			__attribute__((__retain__))
+#else
+# define __retain
+#endif
+
 /* Compiler specific macros. */
 #ifdef __clang__
 #include <linux/compiler-clang.h>

kernel/bpf/verifier.c

@@ -4549,11 +4549,12 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 			state->stack[spi].spilled_ptr.id = 0;
 	} else if (!reg && !(off % BPF_REG_SIZE) && is_bpf_st_mem(insn) &&
 		   env->bpf_capable) {
-		struct bpf_reg_state fake_reg = {};
+		struct bpf_reg_state *tmp_reg = &env->fake_reg[0];
 
-		__mark_reg_known(&fake_reg, insn->imm);
-		fake_reg.type = SCALAR_VALUE;
-		save_register_state(env, state, spi, &fake_reg, size);
+		memset(tmp_reg, 0, sizeof(*tmp_reg));
+		__mark_reg_known(tmp_reg, insn->imm);
+		tmp_reg->type = SCALAR_VALUE;
+		save_register_state(env, state, spi, tmp_reg, size);
 	} else if (reg && is_spillable_regtype(reg->type)) {
 		/* register containing pointer is being spilled into stack */
 		if (size != BPF_REG_SIZE) {
@@ -15113,7 +15114,6 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 	struct bpf_reg_state *regs = this_branch->frame[this_branch->curframe]->regs;
 	struct bpf_reg_state *dst_reg, *other_branch_regs, *src_reg = NULL;
 	struct bpf_reg_state *eq_branch_regs;
-	struct bpf_reg_state fake_reg = {};
 	u8 opcode = BPF_OP(insn->code);
 	bool is_jmp32;
 	int pred = -1;
@@ -15179,7 +15179,8 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 			verbose(env, "BPF_JMP/JMP32 uses reserved fields\n");
 			return -EINVAL;
 		}
-		src_reg = &fake_reg;
+		src_reg = &env->fake_reg[0];
+		memset(src_reg, 0, sizeof(*src_reg));
 		src_reg->type = SCALAR_VALUE;
 		__mark_reg_known(src_reg, insn->imm);
 	}
@@ -15239,10 +15240,16 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 				      &other_branch_regs[insn->src_reg],
 				      dst_reg, src_reg, opcode, is_jmp32);
 	} else /* BPF_SRC(insn->code) == BPF_K */ {
+		/* reg_set_min_max() can mangle the fake_reg. Make a copy
+		 * so that these are two different memory locations. The
+		 * src_reg is not used beyond here in context of K.
+		 */
+		memcpy(&env->fake_reg[1], &env->fake_reg[0],
+		       sizeof(env->fake_reg[0]));
 		err = reg_set_min_max(env,
 				      &other_branch_regs[insn->dst_reg],
-				      src_reg /* fake one */,
-				      dst_reg, src_reg /* same fake one */,
+				      &env->fake_reg[0],
+				      dst_reg, &env->fake_reg[1],
 				      opcode, is_jmp32);
 	}
 	if (err)
@@ -20313,7 +20320,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			goto next_insn;
 		}
 
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
 		/* Implement bpf_get_smp_processor_id() inline. */
 		if (insn->imm == BPF_FUNC_get_smp_processor_id &&
 		    prog->jit_requested && bpf_jit_supports_percpu_insn()) {

net/core/filter.c

@@ -1665,6 +1665,11 @@ static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp);
 static inline int __bpf_try_make_writable(struct sk_buff *skb,
 					  unsigned int write_len)
 {
+#ifdef CONFIG_DEBUG_NET
+	/* Avoid a splat in pskb_may_pull_reason() */
+	if (write_len > INT_MAX)
+		return -EINVAL;
+#endif
 	return skb_ensure_writable(skb, write_len);
 }
 

tools/testing/selftests/bpf/prog_tests/verifier.c

@@ -53,6 +53,7 @@
 #include "verifier_movsx.skel.h"
 #include "verifier_netfilter_ctx.skel.h"
 #include "verifier_netfilter_retcode.skel.h"
+#include "verifier_or_jmp32_k.skel.h"
 #include "verifier_precision.skel.h"
 #include "verifier_prevent_map_lookup.skel.h"
 #include "verifier_raw_stack.skel.h"
@@ -170,6 +171,7 @@ void test_verifier_meta_access(void)          { RUN(verifier_meta_access); }
 void test_verifier_movsx(void)                 { RUN(verifier_movsx); }
 void test_verifier_netfilter_ctx(void)        { RUN(verifier_netfilter_ctx); }
 void test_verifier_netfilter_retcode(void)    { RUN(verifier_netfilter_retcode); }
+void test_verifier_or_jmp32_k(void)           { RUN(verifier_or_jmp32_k); }
 void test_verifier_precision(void)            { RUN(verifier_precision); }
 void test_verifier_prevent_map_lookup(void)   { RUN(verifier_prevent_map_lookup); }
 void test_verifier_raw_stack(void)            { RUN(verifier_raw_stack); }

tools/testing/selftests/bpf/progs/verifier_or_jmp32_k.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+SEC("socket")
+__description("or_jmp32_k: bit ops + branch on unknown value")
+__failure
+__msg("R0 invalid mem access 'scalar'")
+__naked void or_jmp32_k(void)
+{
+	asm volatile ("					\
+	r0 = 0xffffffff;				\
+	r0 /= 1;					\
+	r1 = 0;						\
+	w1 = -1;					\
+	w1 >>= 1;					\
+	w0 &= w1;					\
+	w0 |= 2;					\
+	if w0 != 0x7ffffffd goto l1;			\
+	r0 = 1;						\
+	exit;						\
+l3:							\
+	r0 = 5;						\
+	*(u64*)(r0 - 8) = r0;				\
+	exit;						\
+l2:							\
+	w0 -= 0xe;					\
+	if w0 == 1 goto l3;				\
+	r0 = 4;						\
+	exit;						\
+l1:							\
+	w0 -= 0x7ffffff0;				\
+	if w0 s>= 0xe goto l2;				\
+	r0 = 3;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+char _license[] SEC("license") = "GPL";