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>

3 files changed, 26 insertions, 1 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 50aa87f8d77f..e4070fb02b11 100644
--- a/include/linux/bpf_verifier.h
+++ b/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
 	 */
diff --git a/include/linux/btf.h b/include/linux/btf.h
index f9e56fd12a9f..7c3e40c3295e 100644
--- a/include/linux/btf.h
+++ b/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();							       \
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 93600de3800b..f14c275950b5 100644
--- a/include/linux/compiler_types.h
+++ b/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>