Re: [PATCH bpf] bpf, x64: Fix prog_array_map_poke_run map poke update

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Nov 27, 2023 at 10:45:25AM +0100, Jiri Olsa wrote:
> Lee pointed out issue found by syscaller [0] hitting BUG in prog
> array map poke update in prog_array_map_poke_run function due to
> bpf_arch_text_poke error return value.
> 
> There's race window where bpf_arch_text_poke can fail due to missing
> bpf program kallsym symbols, which is accounted for with check for
> -EINVAL in BUG_ON.
> 
> The problem is that in such case we won't update the tail call jump
> and cause imballance for the next tail call update check which will
> fail with -EBUSY in __bpf_arch_text_poke.
> 
> I'm hitting following race during the program load:
> 
>   CPU 0                                   CPU 1
> 
>   bpf_prog_load
>     bpf_check
>       do_misc_fixups
>         prog_array_map_poke_track {}
> 
>                                           map_update_elem
>                                             bpf_fd_array_map_update_elem
>                                               prog_array_map_poke_run
> 
>                                                 bpf_arch_text_poke returns -EINVAL
> 
>     bpf_prog_kallsyms_add
> 
> After bpf_arch_text_poke (CPU 1) fails to update the tail call jump,
> the next poke update fails on expected jump instruction check in
> __bpf_arch_text_poke with -EBUSY and triggers the BUG_ON in
> prog_array_map_poke_run.
> 
> Similar race exists on the program unload.
> 
> Fixing this by calling directly __bpf_arch_text_poke and skipping the bpf
> symbol check like we do in bpf_tail_call_direct_fixup. This way the
> prog_array_map_poke_run does not depend on bpf program having the kallsym
> symbol in place.
> 
> [0] https://syzkaller.appspot.com/bug?extid=97a4fe20470e9bc30810
> 
> Cc: Lee Jones <lee@kernel.org>
> Cc: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
> Reported-by: syzbot+97a4fe20470e9bc30810@syzkaller.appspotmail.com
> Tested-by: Lee Jones <lee@kernel.org>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

hum, this breaks non x86 builds.. will send new version

jirka


> ---
>  arch/x86/net/bpf_jit_comp.c |  4 ++--
>  include/linux/bpf.h         |  2 ++
>  kernel/bpf/arraymap.c       | 31 +++++++++++--------------------
>  3 files changed, 15 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 8c10d9abc239..35c2988caf29 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -391,8 +391,8 @@ static int emit_jump(u8 **pprog, void *func, void *ip)
>  	return emit_patch(pprog, func, ip, 0xE9);
>  }
>  
> -static int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> -				void *old_addr, void *new_addr)
> +int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> +			 void *old_addr, void *new_addr)
>  {
>  	const u8 *nop_insn = x86_nops[5];
>  	u8 old_insn[X86_PATCH_SIZE];
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 6762dac3ef76..c28a8563e845 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3174,6 +3174,8 @@ enum bpf_text_poke_type {
>  
>  int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
>  		       void *addr1, void *addr2);
> +int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> +			 void *old_addr, void *new_addr);
>  
>  void *bpf_arch_text_copy(void *dst, void *src, size_t len);
>  int bpf_arch_text_invalidate(void *dst, size_t len);
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 2058e89b5ddd..0b5afa2ec17a 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -1044,20 +1044,11 @@ static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
>  			 *    activated, so tail call updates can arrive from here
>  			 *    while JIT is still finishing its final fixup for
>  			 *    non-activated poke entries.
> -			 * 3) On program teardown, the program's kallsym entry gets
> -			 *    removed out of RCU callback, but we can only untrack
> -			 *    from sleepable context, therefore bpf_arch_text_poke()
> -			 *    might not see that this is in BPF text section and
> -			 *    bails out with -EINVAL. As these are unreachable since
> -			 *    RCU grace period already passed, we simply skip them.
> -			 * 4) Also programs reaching refcount of zero while patching
> +			 * 3) Also programs reaching refcount of zero while patching
>  			 *    is in progress is okay since we're protected under
>  			 *    poke_mutex and untrack the programs before the JIT
> -			 *    buffer is freed. When we're still in the middle of
> -			 *    patching and suddenly kallsyms entry of the program
> -			 *    gets evicted, we just skip the rest which is fine due
> -			 *    to point 3).
> -			 * 5) Any other error happening below from bpf_arch_text_poke()
> +			 *    buffer is freed.
> +			 * 4) Any error happening below from __bpf_arch_text_poke()
>  			 *    is a unexpected bug.
>  			 */
>  			if (!READ_ONCE(poke->tailcall_target_stable))
> @@ -1073,33 +1064,33 @@ static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
>  			new_addr = new ? (u8 *)new->bpf_func + poke->adj_off : NULL;
>  
>  			if (new) {
> -				ret = bpf_arch_text_poke(poke->tailcall_target,
> +				ret = __bpf_arch_text_poke(poke->tailcall_target,
>  							 BPF_MOD_JUMP,
>  							 old_addr, new_addr);
> -				BUG_ON(ret < 0 && ret != -EINVAL);
> +				BUG_ON(ret < 0);
>  				if (!old) {
> -					ret = bpf_arch_text_poke(poke->tailcall_bypass,
> +					ret = __bpf_arch_text_poke(poke->tailcall_bypass,
>  								 BPF_MOD_JUMP,
>  								 poke->bypass_addr,
>  								 NULL);
> -					BUG_ON(ret < 0 && ret != -EINVAL);
> +					BUG_ON(ret < 0);
>  				}
>  			} else {
> -				ret = bpf_arch_text_poke(poke->tailcall_bypass,
> +				ret = __bpf_arch_text_poke(poke->tailcall_bypass,
>  							 BPF_MOD_JUMP,
>  							 old_bypass_addr,
>  							 poke->bypass_addr);
> -				BUG_ON(ret < 0 && ret != -EINVAL);
> +				BUG_ON(ret < 0);
>  				/* let other CPUs finish the execution of program
>  				 * so that it will not possible to expose them
>  				 * to invalid nop, stack unwind, nop state
>  				 */
>  				if (!ret)
>  					synchronize_rcu();
> -				ret = bpf_arch_text_poke(poke->tailcall_target,
> +				ret = __bpf_arch_text_poke(poke->tailcall_target,
>  							 BPF_MOD_JUMP,
>  							 old_addr, NULL);
> -				BUG_ON(ret < 0 && ret != -EINVAL);
> +				BUG_ON(ret < 0);
>  			}
>  		}
>  	}
> -- 
> 2.43.0
>