[PATCH bpf-next v4 3/4] bpf, x86: Emit ENDBR for indirect jump targets

[Xu Kuohai]

From: Xu Kuohai <xukuohai at huawei.com>

On CPUs that support CET/IBT, the indirect jump selftest triggers
a kernel panic because the indirect jump targets lack ENDBR
instructions.

To fix it, emit an ENDBR instruction to each indirect jump target. Since
the ENDBR instruction shifts the position of original jited instructions,
fix the instruction address calculation wherever the addresses are used.

For reference, below is a sample panic log.

 Missing ENDBR: bpf_prog_2e5f1c71c13ac3e0_big_jump_table+0x97/0xe1
 ------------[ cut here ]------------
 kernel BUG at arch/x86/kernel/cet.c:133!
 Oops: invalid opcode: 0000 [#1] SMP NOPTI

 ...

  ? 0xffffffffc00fb258
  ? bpf_prog_2e5f1c71c13ac3e0_big_jump_table+0x97/0xe1
  bpf_prog_test_run_syscall+0x110/0x2f0
  ? fdget+0xba/0xe0
  __sys_bpf+0xe4b/0x2590
  ? __kmalloc_node_track_caller_noprof+0x1c7/0x680
  ? bpf_prog_test_run_syscall+0x215/0x2f0
  __x64_sys_bpf+0x21/0x30
  do_syscall_64+0x85/0x620
  ? bpf_prog_test_run_syscall+0x1e2/0x2f0

Fixes: 493d9e0d6083 ("bpf, x86: add support for indirect jumps")
Signed-off-by: Xu Kuohai <xukuohai at huawei.com>
---
 arch/x86/net/bpf_jit_comp.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index e3b1c4b1d550..ef79baac42d7 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1733,6 +1733,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
 				dst_reg = X86_REG_R9;
 		}
 
+		if (bpf_insn_is_indirect_target(bpf_prog, i - 1))
+			EMIT_ENDBR();
+
 		switch (insn->code) {
 			/* ALU */
 		case BPF_ALU | BPF_ADD | BPF_X:
@@ -2439,7 +2442,7 @@ st:			if (is_imm8(insn->off))
 
 			/* call */
 		case BPF_JMP | BPF_CALL: {
-			u8 *ip = image + addrs[i - 1];
+			u8 *ip = image + addrs[i - 1] + (prog - temp);
 
 			func = (u8 *) __bpf_call_base + imm32;
 			if (src_reg == BPF_PSEUDO_CALL && tail_call_reachable) {
@@ -2464,7 +2467,8 @@ st:			if (is_imm8(insn->off))
 			if (imm32)
 				emit_bpf_tail_call_direct(bpf_prog,
 							  &bpf_prog->aux->poke_tab[imm32 - 1],
-							  &prog, image + addrs[i - 1],
+							  &prog,
+							  image + addrs[i - 1] + (prog - temp),
 							  callee_regs_used,
 							  stack_depth,
 							  ctx);
@@ -2473,7 +2477,7 @@ st:			if (is_imm8(insn->off))
 							    &prog,
 							    callee_regs_used,
 							    stack_depth,
-							    image + addrs[i - 1],
+							    image + addrs[i - 1] + (prog - temp),
 							    ctx);
 			break;
 
@@ -2638,7 +2642,8 @@ st:			if (is_imm8(insn->off))
 			break;
 
 		case BPF_JMP | BPF_JA | BPF_X:
-			emit_indirect_jump(&prog, insn->dst_reg, image + addrs[i - 1]);
+			emit_indirect_jump(&prog, insn->dst_reg,
+					   image + addrs[i - 1] + (prog - temp));
 			break;
 		case BPF_JMP | BPF_JA:
 		case BPF_JMP32 | BPF_JA:
@@ -2728,7 +2733,7 @@ st:			if (is_imm8(insn->off))
 			ctx->cleanup_addr = proglen;
 			if (bpf_prog_was_classic(bpf_prog) &&
 			    !ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN)) {
-				u8 *ip = image + addrs[i - 1];
+				u8 *ip = image + addrs[i - 1] + (prog - temp);
 
 				if (emit_spectre_bhb_barrier(&prog, ip, bpf_prog))
 					return -EINVAL;
-- 
2.47.3