The plumbing for offline unwinding when we throw an exception in
programs would require walking the stack, hence introduce a new
arch_bpf_stack_walk function. This is provided when the JIT supports
exceptions, i.e. bpf_jit_supports_exceptions is true. The arch-specific
code is really minimal, hence it should straightforward to extend this
support to other architectures as well, as it reuses the logic of
arch_stack_walk, but allowing access to unwind_state data.
Once the stack pointer and frame pointer are known for the main subprog
during the unwinding, we know the stack layout and location of any
callee-saved registers which must be restored before we return back to
the kernel.
This handling will be added in the next patch.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 21 +++++++++++++++++++++
include/linux/filter.h | 2 ++
kernel/bpf/core.c | 9 +++++++++
3 files changed, 32 insertions(+)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 438adb695daa..d326503ce242 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -16,6 +16,7 @@
#include <asm/set_memory.h>
#include <asm/nospec-branch.h>
#include <asm/text-patching.h>
+#include <asm/unwind.h>
static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len)
{
@@ -2660,3 +2661,23 @@ void bpf_jit_free(struct bpf_prog *prog)
bpf_prog_unlock_free(prog);
}
+
+bool bpf_jit_supports_exceptions(void)
+{
+ return IS_ENABLED(CONFIG_UNWINDER_ORC) || IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER);
+}
+
+void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie)
+{
+#if defined(CONFIG_UNWINDER_ORC) || defined(CONFIG_UNWINDER_FRAME_POINTER)
+ struct unwind_state state;
+ unsigned long addr;
+
+ for (unwind_start(&state, current, NULL, NULL); !unwind_done(&state);
+ unwind_next_frame(&state)) {
+ addr = unwind_get_return_address(&state);
+ if (!addr || !consume_fn(cookie, (u64)addr, (u64)state.sp, (u64)state.bp))
+ break;
+ }
+#endif
+}
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f69114083ec7..21ac801330bb 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -920,6 +920,8 @@ bool bpf_jit_needs_zext(void);
bool bpf_jit_supports_subprog_tailcalls(void);
bool bpf_jit_supports_kfunc_call(void);
bool bpf_jit_supports_far_kfunc_call(void);
+bool bpf_jit_supports_exceptions(void);
+void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie);
bool bpf_helper_changes_pkt_data(void *func);
static inline bool bpf_dump_raw_ok(const struct cred *cred)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5c484b2bc3d6..5e224cf0ec27 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2770,6 +2770,15 @@ int __weak bpf_arch_text_invalidate(void *dst, size_t len)
return -ENOTSUPP;
}
+bool __weak bpf_jit_supports_exceptions(void)
+{
+ return false;
+}
+
+void __weak arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie)
+{
+}
+
#ifdef CONFIG_BPF_SYSCALL
static int __init bpf_global_ma_init(void)
{
--
2.40.1
