[RFC,05/12] ebpf/uBPF: Add qemu_prepare_ubpf to load ebpf binary

Commit Message

Zhang Chen June 17, 2022, 7:36 a.m. UTC

The qemu_prepare_ubpf() can load user defined userspace ebpf binary
file to Qemu userspace ebpf VM but not run it. The ebpf program
will triggered in the hook point.

Signed-off-by: Zhang Chen <[e-mail]>
---
 ebpf/ubpf-stub.c |   5 +++
 ebpf/ubpf.c      | 100 +++++++++++++++++++++++++++++++++++++++++++++++
 ebpf/ubpf.h      |   1 +
 3 files changed, 106 insertions(+)

Patch

diff --git a/ebpf/ubpf-stub.c b/ebpf/ubpf-stub.c
index 2e8bf15b91..885bd954b7 100644
--- a/ebpf/ubpf-stub.c
+++ b/ebpf/ubpf-stub.c
@@ -22,3 +22,8 @@  bool qemu_ubpf_read_target(UbpfState *u_ebpf, char *path)
 }
 
 void qemu_ubpf_init_jit(UbpfState *u_ebpf, bool jit) {}
+
+int qemu_ubpf_prepare(UbpfState *u_ebpf, char *code_path)
+{
+    return 0;
+}
diff --git a/ebpf/ubpf.c b/ebpf/ubpf.c
index 38a6530903..d65fffeda3 100644
--- a/ebpf/ubpf.c
+++ b/ebpf/ubpf.c
@@ -99,3 +99,103 @@  void qemu_ubpf_init_jit(UbpfState *u_ebpf, bool jit)
 {
     u_ebpf->jit = jit;
 }
+
+static uint64_t gather_bytes(uint8_t a, uint8_t b, uint8_t c,
+                             uint8_t d, uint8_t e)
+{
+    return ((uint64_t)a << 32) |
+           ((uint32_t)b << 24) |
+           ((uint32_t)c << 16) |
+           ((uint16_t)d << 8) |
+           e;
+}
+
+static void trash_registers(void)
+{
+    /* Overwrite all caller-save registers */
+    asm(
+        "mov $0xf0, %rax;"
+        "mov $0xf1, %rcx;"
+        "mov $0xf2, %rdx;"
+        "mov $0xf3, %rsi;"
+        "mov $0xf4, %rdi;"
+        "mov $0xf5, %r8;"
+        "mov $0xf6, %r9;"
+        "mov $0xf7, %r10;"
+        "mov $0xf8, %r11;"
+    );
+}
+
+static uint32_t sqrti(uint32_t x)
+{
+    return sqrt(x);
+}
+
+static uint64_t unwind(uint64_t i)
+{
+    return i;
+}
+
+static void register_functions(struct ubpf_vm *vm)
+{
+    ubpf_register(vm, 0, "gather_bytes", gather_bytes);
+    ubpf_register(vm, 1, "memfrob", memfrob);
+    ubpf_register(vm, 2, "trash_registers", trash_registers);
+    ubpf_register(vm, 3, "sqrti", sqrti);
+    ubpf_register(vm, 4, "strcmp_ext", strcmp);
+    ubpf_register(vm, 5, "unwind", unwind);
+    ubpf_set_unwind_function_index(vm, 5);
+}
+
+int qemu_ubpf_prepare(UbpfState *u_ebpf, char *code_path)
+{
+    bool is_elf;
+    char *errmsg;
+    int ret;
+
+    if (!qemu_ubpf_read_code(u_ebpf, code_path)) {
+        error_report("Ubpf failed to read code");
+        return -1;
+    }
+
+    u_ebpf->vm = ubpf_create();
+    if (!u_ebpf->vm) {
+        error_report("Failed to create ubpf VM");
+        return -1;
+    }
+
+    register_functions(u_ebpf->vm);
+
+    /*
+     * The ELF magic corresponds to an RSH instruction with an offset,
+     * which is invalid.
+     */
+     is_elf = u_ebpf->code_len >= SELFMAG && !memcmp(u_ebpf->code,
+                                                     ELFMAG, SELFMAG);
+
+    if (is_elf) {
+        ret = ubpf_load_elf(u_ebpf->vm, u_ebpf->code,
+                            u_ebpf->code_len, &errmsg);
+    } else {
+        ret = ubpf_load(u_ebpf->vm, u_ebpf->code,
+                        u_ebpf->code_len, &errmsg);
+    }
+
+    if (ret < 0) {
+        error_report("Failed to load ubpf code: %s ", errmsg);
+        free(errmsg);
+        ubpf_destroy(u_ebpf->vm);
+        return -1;
+    }
+
+    if (u_ebpf->jit) {
+        u_ebpf->fn = ubpf_compile(u_ebpf->vm, &errmsg);
+        if (u_ebpf->fn == NULL) {
+            error_report("Failed to ubpf compile: %s", errmsg);
+            free(errmsg);
+            return -1;
+        }
+    }
+
+    return 0;
+}
diff --git a/ebpf/ubpf.h b/ebpf/ubpf.h
index 808c02565c..9a35efbeb6 100644
--- a/ebpf/ubpf.h
+++ b/ebpf/ubpf.h
@@ -37,5 +37,6 @@  typedef struct UbpfState {
 bool qemu_ubpf_read_code(UbpfState *u_ebpf, char *path);
 bool qemu_ubpf_read_target(UbpfState *u_ebpf, char *path);
 void qemu_ubpf_init_jit(UbpfState *u_ebpf, bool jit);
+int qemu_ubpf_prepare(UbpfState *u_ebpf, char *code_path);
 
 #endif /* QEMU_UBPF_H */