[PATCH bpf v2] bpf: verifier: reject addr_space_cast insn without arena

[PATCH bpf v2] bpf: verifier: reject addr_space_cast insn without arena

[Puranjay Mohan]

The verifier allows using the addr_space_cast instruction in a program
that doesn't have an associated arena. This was caught in the form an
invalid memory access in do_misc_fixups() when while converting
addr_space_cast to a normal 32-bit mov, env->prog->aux->arena was
dereferenced to check for BPF_F_NO_USER_CONV flag.

Reject programs that include the addr_space_cast instruction but don't
have an associated arena.

root@rv-tester:~# ./reproducer
 Unable to handle kernel access to user memory without uaccess routines at virtual address 0000000000000030
 Oops [#1]
 Modules linked in: sch_fq_codel drm fuse i2c_core drm_panel_orientation_quirks backlight configfs ip_tables x_tables
 CPU: 2 PID: 265 Comm: reproducer Not tainted 6.8.0 #3
 Hardware name: riscv-virtio,qemu (DT)
 epc : do_misc_fixups+0x43c/0x1168
  ra : bpf_check+0xda8/0x22b6
 epc : ffffffff8017eeaa ra : ffffffff801936d6 sp : ff200000011bb890
  gp : ffffffff82293468 tp : ff60000084fcb840 t0 : ff60000084e38048
  t1 : 0000000000000048 t2 : ff5fffff80000000 s0 : ff200000011bba60
  s1 : ff2000000101d058 a0 : ff6000008b980000 a1 : 0000000000000004
  a2 : 00000000000000e1 a3 : 0000000000000001 a4 : 0000000000010000
  a5 : 0000000000000000 a6 : 0000000000000001 a7 : ff2000000101d000
  s2 : 0000000000000002 s3 : 0000000000000000 s4 : 0000000000000000
  s5 : 0000000000000002 s6 : 0000000000000000 s7 : ff6000008b980aa0
  s8 : 0000000000010005 s9 : 0000000000000004 s10: ff6000008b980000
  s11: 0000000000000000 t3 : 0000000000002000 t4 : 0000ff0000000000
  t5 : 00ff000000000000 t6 : ff20000000000000
 status: 0000000200000120 badaddr: 0000000000000030 cause: 000000000000000d
 [<ffffffff8017eeaa>] do_misc_fixups+0x43c/0x1168
 [<ffffffff801936d6>] bpf_check+0xda8/0x22b6
 [<ffffffff80174b32>] bpf_prog_load+0x486/0x8dc
 [<ffffffff80176566>] __sys_bpf+0xbd8/0x214e
 [<ffffffff80177d14>] __riscv_sys_bpf+0x22/0x2a
 [<ffffffff80d2493a>] do_trap_ecall_u+0x102/0x17c
 [<ffffffff80d3048c>] ret_from_exception+0x0/0x64
 Code: b345 9783 0024 4685 8b63 16d7 3783 008d 7f9c 7fdc (5b9c) 83c9
 ---[ end trace 0000000000000000 ]---
 Kernel panic - not syncing: Fatal exception
 SMP: stopping secondary CPUs

Fixes: 6082b6c328b5 ("bpf: Recognize addr_space_cast instruction in the verifier.")
Reported-by: xingwei lee <xrivendell7@gmail.com>
Reported-by: yue sun <samsun1006219@gmail.com>
Closes: https://lore.kernel.org/bpf/CABOYnLz09O1+2gGVJuCxd_24a-7UueXzV-Ff+Fr+h5EKFDiYCQ@mail.gmail.com/
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
---
Changes in V2:
V1: https://lore.kernel.org/bpf/20240322143829.40808-1-puranjay12@gmail.com/
- Reject programs that have the addr_space_cast instruction without an
  arena rather than checking for a NULL pointer in do_misc_fixups.
---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ca6cacf7b42f..7d0bbee10d71 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14014,6 +14014,10 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 					verbose(env, "addr_space_cast insn can only convert between address space 1 and 0\n");
 					return -EINVAL;
 				}
+				if (!env->prog->aux->arena) {
+					verbose(env, "addr_space_cast insn can only be used in a program that has an associated arena\n");
+					return -EINVAL;
+				}
 			} else {
 				if ((insn->off != 0 && insn->off != 8 && insn->off != 16 &&
 				     insn->off != 32) || insn->imm) {
-- 
2.40.1

Re: [PATCH bpf v2] bpf: verifier: reject addr_space_cast insn without arena

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Fri, 22 Mar 2024 15:35:18 +0000 you wrote:
> The verifier allows using the addr_space_cast instruction in a program
> that doesn't have an associated arena. This was caught in the form an
> invalid memory access in do_misc_fixups() when while converting
> addr_space_cast to a normal 32-bit mov, env->prog->aux->arena was
> dereferenced to check for BPF_F_NO_USER_CONV flag.
> 
> Reject programs that include the addr_space_cast instruction but don't
> have an associated arena.
> 
> [...]

Here is the summary with links:
  - [bpf,v2] bpf: verifier: reject addr_space_cast insn without arena
    https://git.kernel.org/bpf/bpf/c/122fdbd2a030

You are awesome, thank you!
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