[PATCH bpf-next v6 2/9] bpf: add BPF_JIT_KASAN for KASAN instrumentation of JITed programs

Add a new Kconfig option CONFIG_BPF_JIT_KASAN that automatically enables
generic KASAN (Kernel Address SANitizer) memory access checks for
JIT-compiled BPF programs as well, when both KASAN (and more
specifically, generic KASAN with KASAN_VMALLOC) and JIT compiler are
enabled. This new Kconfig is not a user selectable one: it is
automatically enabled if KASAN is enabled on a compatible platform. When
enabled, the JIT compiler will emit shadow memory checks before memory
loads and stores to detect use-after-free or out-of-bounds accesses at
runtime. The option is gated behind HAVE_EBPF_JIT_KASAN, as it needs
proper arch-specific implementation.

Acked-by: Andrey Konovalov <[email protected]>
Acked-by: Ihor Solodrai <[email protected]>
Signed-off-by: Alexis Lothoré (eBPF Foundation) <[email protected]>
---
Changes in v6:
- fix commit msg
- get rid of "if KASAN" when setting default value, already implied by
  KASAN_GENERIC

Changes in v4:
- reorganize dependencies (Andrey)
- drop VMAP_STACK dependency

Changes in v2:
- add dependency on kasan for vmalloc and vmalloc'ed stack
---
 kernel/bpf/Kconfig | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index eb3de35734f0..d7d25477ef48 100644
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -17,6 +17,10 @@ config HAVE_CBPF_JIT
 config HAVE_EBPF_JIT
 	bool
 
+# KASAN support for JIT compiler
+config HAVE_EBPF_JIT_KASAN
+	bool
+
 # Used by archs to tell that they want the BPF JIT compiler enabled by
 # default for kernels that were compiled with BPF JIT support.
 config ARCH_WANT_DEFAULT_BPF_JIT
@@ -101,4 +105,17 @@ config BPF_LSM
 
 	  If you are unsure how to answer this question, answer N.
 
+config BPF_JIT_KASAN
+	bool
+	depends on HAVE_EBPF_JIT_KASAN
+	depends on KASAN_GENERIC
+	depends on KASAN_VMALLOC
+	depends on BPF_JIT
+	default y
+	help
+	  Makes JIT compiler insert generic outline KASAN checks in BPF
+	  programs when they are inserted in the kernel. This feature is
+	  automatically enabled if the needed set of KASAN and BPF
+	  configuration options is enabled.
+
 endmenu # "BPF subsystem"

-- 
2.55.0