On 8/6/25 1:58 AM, Puranjay Mohan wrote:
Begin reporting arena page faults and the faulting address to BPF
program's stderr, this patch adds support in the arm64 and x86-64 JITs,
support for other archs can be added later.
The fault handlers receive the 32 bit address in the arena region so
the upper 32 bits of user_vm_start is added to it before printing the
address. This is what the user would expect to see as this is what is
printed by bpf_printk() is you pass it an address returned by
bpf_arena_alloc_pages();
Signed-off-by: Puranjay Mohan <puranjay@xxxxxxxxxx>
LGTM with some nits below.
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
arch/arm64/net/bpf_jit_comp.c | 31 ++++++++++++++
arch/x86/net/bpf_jit_comp.c | 80 +++++++++++++++++++++++++++++++++--
include/linux/bpf.h | 1 +
kernel/bpf/arena.c | 20 +++++++++
4 files changed, 128 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 42643fd9168fc..5680c7cd8932f 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1066,6 +1066,9 @@ static void build_epilogue(struct jit_ctx *ctx, bool was_classic)
emit(A64_RET(A64_LR), ctx);
}
+#define BPF_FIXUP_LOAD_OFFSET_MASK GENMASK(15, 0)
+#define BPF_FIXUP_ARENA_REG_MASK GENMASK(20, 16)
+#define BPF_ARENA_ACCESS BIT(21)
#define BPF_FIXUP_REG_MASK GENMASK(31, 27)
#define DONT_CLEAR 5 /* Unused ARM64 register from BPF's POV */
@@ -1073,11 +1076,22 @@ bool ex_handler_bpf(const struct exception_table_entry *ex,
struct pt_regs *regs)
{
int dst_reg = FIELD_GET(BPF_FIXUP_REG_MASK, ex->fixup);
+ s16 off = FIELD_GET(BPF_FIXUP_LOAD_OFFSET_MASK, ex->fixup);
+ int arena_reg = FIELD_GET(BPF_FIXUP_ARENA_REG_MASK, ex->fixup);
+ bool is_arena = !!(ex->fixup & BPF_ARENA_ACCESS);
+ bool is_write = (dst_reg == DONT_CLEAR);
+ unsigned long addr;
if (dst_reg != DONT_CLEAR)
regs->regs[dst_reg] = 0;
/* Skip the faulting instruction */
regs->pc += AARCH64_INSN_SIZE;
+
+ if (is_arena) {
+ addr = regs->regs[arena_reg] + off;
+ bpf_prog_report_arena_violation(is_write, addr);
+ }
+
return true;
}
@@ -1087,6 +1101,9 @@ static int add_exception_handler(const struct bpf_insn *insn,
int dst_reg)
{
off_t ins_offset;
+ s16 load_off = insn->off;
Change 'load_off' to 'off' so it matches the usage in ex_handler_bpf().
Also 'off' could mean the off for a store insn, right?
+ bool is_arena;
+ int arena_reg;
unsigned long pc;
struct exception_table_entry *ex;
@@ -1100,6 +1117,9 @@ static int add_exception_handler(const struct bpf_insn *insn,
BPF_MODE(insn->code) != BPF_PROBE_ATOMIC)
return 0;
+ is_arena = (BPF_MODE(insn->code) == BPF_PROBE_MEM32) ||
+ (BPF_MODE(insn->code) == BPF_PROBE_ATOMIC);
+
if (!ctx->prog->aux->extable ||
WARN_ON_ONCE(ctx->exentry_idx >= ctx->prog->aux->num_exentries))
return -EINVAL;
@@ -1131,6 +1151,17 @@ static int add_exception_handler(const struct bpf_insn *insn,
ex->fixup = FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg);
+ if (is_arena) {
+ ex->fixup |= BPF_ARENA_ACCESS;
+ if (BPF_CLASS(insn->code) == BPF_LDX)
+ arena_reg = bpf2a64[insn->src_reg];
+ else
+ arena_reg = bpf2a64[insn->dst_reg];
+
+ ex->fixup |= FIELD_PREP(BPF_FIXUP_LOAD_OFFSET_MASK, load_off) |
+ FIELD_PREP(BPF_FIXUP_ARENA_REG_MASK, arena_reg);
+ }
+
ex->type = EX_TYPE_BPF;
ctx->exentry_idx++;
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 7e3fca1646203..c8d99375e6de7 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -8,6 +8,7 @@
#include <linux/netdevice.h>
#include <linux/filter.h>
#include <linux/if_vlan.h>
+#include <linux/bitfield.h>
#include <linux/bpf.h>
#include <linux/memory.h>
#include <linux/sort.h>
@@ -1388,16 +1389,67 @@ static int emit_atomic_ld_st_index(u8 **pprog, u32 atomic_op, u32 size,
return 0;
}
+/*
+ * Metadata encoding for exception handling in JITed code.
+ *
+ * Format of `fixup` and `data` fields in `struct exception_table_entry`:
+ *
+ * Bit layout of `fixup` (32-bit):
+ *
+ * +-----------+--------+-----------+---------+----------+
+ * | 31 | 30-24 | 23-16 | 15-8 | 7-0 |
+ * | | | | | |
+ * | ARENA_ACC | Unused | ARENA_REG | DST_REG | INSN_LEN |
+ * +-----------+--------+-----------+---------+----------+
+ *
+ * - INSN_LEN (8 bits): Length of faulting insn (max x86 insn = 15 bytes (fits in 8 bits)).
+ * - DST_REG (8 bits): Offset of dst_reg from reg2pt_regs[] (max offset = 112 (fits in 8 bits)).
+ * This is set to DONT_CLEAR if the insn is a store.
+ * - ARENA_REG (8 bits): Offset of the register that is used to calculate the
+ * address for load/store when accessing the arena region.
+ * - ARENA_ACCESS (1 bit): This bit is set when the faulting instruction accessed the arena region.
+ *
+ * Bit layout of `data` (32-bit):
+ *
+ * +--------------+--------+--------------+
+ * | 31-16 | 15-8 | 7-0 |
+ * | | | |
+ * | ARENA_OFFSET | Unused | EX_TYPE_BPF |
+ * +--------------+--------+--------------+
+ *
+ * - ARENA_OFFSET (16 bits): Offset used to calculate the address for load/store when
+ * accessing the arena region.
+ */
+
#define DONT_CLEAR 1
+#define FIXUP_OFFSET_MASK GENMASK(7, 0)
Maybe FIXUP_INSN_LEN_MASK?
+#define FIXUP_REG_MASK GENMASK(15, 8)
+#define FIXUP_ARENA_REG_MASK GENMASK(23, 16)
+#define FIXUP_ARENA_ACCESS BIT(31)
+#define DATA_ARENA_OFFSET_MASK GENMASK(31, 16)
bool ex_handler_bpf(const struct exception_table_entry *x, struct pt_regs *regs)
{
- u32 reg = x->fixup >> 8;
+ u32 reg = FIELD_GET(FIXUP_REG_MASK, x->fixup);
+ off_t offset = FIELD_GET(FIXUP_OFFSET_MASK, x->fixup);
insn_len = ...
+ bool is_arena = !!(x->fixup & FIXUP_ARENA_ACCESS);
+ bool is_write = (reg == DONT_CLEAR);
+ unsigned long addr;
+ s16 arena_offset;
This should be just 'off', right? It would be good if the terminology is consistent
between different architectures.
+ u32 arena_reg;
/* jump over faulting load and clear dest register */
if (reg != DONT_CLEAR)
*(unsigned long *)((void *)regs + reg) = 0;
- regs->ip += x->fixup & 0xff;
+ regs->ip += offset;
+
+ if (is_arena) {
+ arena_reg = FIELD_GET(FIXUP_ARENA_REG_MASK, x->data);
+ arena_offset = FIELD_GET(DATA_ARENA_OFFSET_MASK, x->data);
+ addr = *(unsigned long *)((void *)regs + arena_reg) + arena_offset;
+ bpf_prog_report_arena_violation(is_write, addr);
+ }
+
return true;
}
@@ -2070,6 +2122,9 @@ st: if (is_imm8(insn->off))
{
struct exception_table_entry *ex;
u8 *_insn = image + proglen + (start_of_ldx - temp);
+ bool is_arena;
+ u32 fixup_reg;
+ u32 arena_reg;
the above two variables can be in the same line and can before 'is_arena'.
s64 delta;
if (!bpf_prog->aux->extable)
@@ -2089,8 +2144,25 @@ st: if (is_imm8(insn->off))
ex->data = EX_TYPE_BPF;
- ex->fixup = (prog - start_of_ldx) |
- ((BPF_CLASS(insn->code) == BPF_LDX ? reg2pt_regs[dst_reg] : DONT_CLEAR) << 8);
+ is_arena = (BPF_MODE(insn->code) == BPF_PROBE_MEM32) ||
+ (BPF_MODE(insn->code) == BPF_PROBE_ATOMIC);
+
+ fixup_reg = (BPF_CLASS(insn->code) == BPF_LDX) ?
+ reg2pt_regs[dst_reg] : DONT_CLEAR;
+
+ ex->fixup = FIELD_PREP(FIXUP_OFFSET_MASK, prog - start_of_ldx) |
+ FIELD_PREP(FIXUP_REG_MASK, fixup_reg);
+
+ if (is_arena) {
+ ex->fixup |= FIXUP_ARENA_ACCESS;
+ if (BPF_CLASS(insn->code) == BPF_LDX)
+ arena_reg = reg2pt_regs[src_reg];
+ else
+ arena_reg = reg2pt_regs[dst_reg];
+
+ ex->fixup |= FIELD_PREP(FIXUP_ARENA_REG_MASK, arena_reg);
+ ex->data |= FIELD_PREP(DATA_ARENA_OFFSET_MASK, insn->off);
+ }
}
break;
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cc700925b802f..3e62834726a97 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3653,6 +3653,7 @@ int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...);
int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
enum bpf_stream_id stream_id);
int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss);
+void bpf_prog_report_arena_violation(bool write, unsigned long addr);
#define bpf_stream_printk(ss, ...) bpf_stream_stage_printk(&ss, __VA_ARGS__)
#define bpf_stream_dump_stack(ss) bpf_stream_stage_dump_stack(&ss)
diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index 5b37753799d20..a1653d1c04ca5 100644
--- a/kernel/bpf/arena.c
+++ b/kernel/bpf/arena.c
@@ -633,3 +633,23 @@ static int __init kfunc_init(void)
return register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, &common_kfunc_set);
}
late_initcall(kfunc_init);
+
+void bpf_prog_report_arena_violation(bool write, unsigned long addr)
+{
+ struct bpf_stream_stage ss;
+ struct bpf_prog *prog;
+ u64 user_vm_start;
+
+ prog = bpf_prog_find_from_stack();
+ if (!prog)
+ return;
+
+ user_vm_start = bpf_arena_get_user_vm_start(prog->aux->arena);
+ addr += (user_vm_start >> 32) << 32;
+
+ bpf_stream_stage(ss, prog, BPF_STDERR, ({
+ bpf_stream_printk(ss, "ERROR: Arena %s access at unmapped address 0x%lx\n",
+ write ? "WRITE" : "READ", addr);
+ bpf_stream_dump_stack(ss);
+ }));
+}
