netdev - Re: [PATCH bpf-next 12/15] bpf: Preserve boundaries and track scalars on narrowing fill

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Tue, 26 Dec 2023 13:29:07 +0800
From: Shung-Hsi Yu <shung-hsi.yu@...e.com>
To: Maxim Mikityanskiy <maxtram95@...il.com>
Cc: Eduard Zingerman <eddyz87@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	netdev@...r.kernel.org, Maxim Mikityanskiy <maxim@...valent.com>
Subject: Re: [PATCH bpf-next 12/15] bpf: Preserve boundaries and track
 scalars on narrowing fill

On Wed, Dec 20, 2023 at 11:40:10PM +0200, Maxim Mikityanskiy wrote:
> When the width of a fill is smaller than the width of the preceding
> spill, the information about scalar boundaries can still be preserved,
> as long as it's coerced to the right width (done by coerce_reg_to_size).
> Even further, if the actual value fits into the fill width, the ID can
> be preserved as well for further tracking of equal scalars.
> 
> Implement the above improvements, which makes narrowing fills behave the
> same as narrowing spills and MOVs between registers.
> 
> Two tests are adjusted to accommodate for endianness differences and to
> take into account that it's now allowed to do a narrowing fill from the
> least significant bits.
> 
> reg_bounds_sync is added to coerce_reg_to_size to correctly adjust
> umin/umax boundaries after the var_off truncation, for example, a 64-bit
> value 0xXXXXXXXX00000000, when read as a 32-bit, gets umin = 0, umax =
> 0xFFFFFFFF, var_off = (0x0; 0xffffffff00000000), which needs to be
> synced down to umax = 0, otherwise reg_bounds_sanity_check doesn't pass.
> 
> Signed-off-by: Maxim Mikityanskiy <maxim@...valent.com>
> ---
>  kernel/bpf/verifier.c                         | 20 ++++++++++---
>  .../selftests/bpf/progs/verifier_spill_fill.c | 28 +++++++++++++------
>  2 files changed, 35 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9b5053389739..b6e252539e52 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4772,7 +4772,13 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
>  			if (dst_regno < 0)
>  				return 0;
>  
> -			if (!(off % BPF_REG_SIZE) && size == spill_size) {
> +			if (size <= spill_size &&
> +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> +			    !(off % BPF_REG_SIZE)
> +#else
> +			    !((off + size - spill_size) % BPF_REG_SIZE)
> +#endif

If I understand correctly, it is preferred to keep endianess checking
macro out of verfier.c and have helper function handle them instead.

E.g. See bpf_ctx_narrow_access_offset() from include/linux/filter.h

> [...]