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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a6fcf48b4ddsm377080466b.67.2024.06.24.00.15.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Jun 2024 00:15:50 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 24 Jun 2024 09:15:48 +0200 To: Shung-Hsi Yu Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Yonghong Song Subject: Re: [PATCH bpf-next 2/2] bpf: verifier: use check_sub_overflow() to check for subtraction overflows Message-ID: References: <20240623070324.12634-1-shung-hsi.yu@suse.com> <20240623070324.12634-3-shung-hsi.yu@suse.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240623070324.12634-3-shung-hsi.yu@suse.com> On Sun, Jun 23, 2024 at 03:03:20PM +0800, Shung-Hsi Yu wrote: SNIP > @@ -13428,15 +13409,16 @@ static void scalar_min_max_sub(struct bpf_reg_state *dst_reg, > s64 smax_val = src_reg->smax_value; > u64 umin_val = src_reg->umin_value; > u64 umax_val = src_reg->umax_value; > + s64 smin_cur, smax_cur; > > - if (signed_sub_overflows(dst_reg->smin_value, smax_val) || > - signed_sub_overflows(dst_reg->smax_value, smin_val)) { > + if (check_sub_overflow(dst_reg->smin_value, smax_val, &smin_cur) || > + check_sub_overflow(dst_reg->smax_value, smin_val, &smax_cur)) { > /* Overflow possible, we know nothing */ > dst_reg->smin_value = S64_MIN; > dst_reg->smax_value = S64_MAX; > } else { > - dst_reg->smin_value -= smax_val; > - dst_reg->smax_value -= smin_val; > + dst_reg->smin_value = smin_cur; > + dst_reg->smax_value = smax_cur; > } > if (dst_reg->umin_value < umax_val) { > /* Overflow possible, we know nothing */ > -- > 2.45.2 > > could we use dst_reg->smin_* pointers directly as the sum pointer arguments in check_add_overflow ? ditto for the check_sub_overflow in the other change jirka --- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 3f6be4923655..dbb99818e938 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -12720,26 +12720,6 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, return 0; } -static bool signed_add_overflows(s64 a, s64 b) -{ - /* Do the add in u64, where overflow is well-defined */ - s64 res = (s64)((u64)a + (u64)b); - - if (b < 0) - return res > a; - return res < a; -} - -static bool signed_add32_overflows(s32 a, s32 b) -{ - /* Do the add in u32, where overflow is well-defined */ - s32 res = (s32)((u32)a + (u32)b); - - if (b < 0) - return res > a; - return res < a; -} - static bool signed_sub_overflows(s64 a, s64 b) { /* Do the sub in u64, where overflow is well-defined */ @@ -13241,21 +13221,15 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, * added into the variable offset, and we copy the fixed offset * from ptr_reg. */ - if (signed_add_overflows(smin_ptr, smin_val) || - signed_add_overflows(smax_ptr, smax_val)) { + if (check_add_overflow(smin_ptr, smin_val, &dst_reg->smin_value) || + check_add_overflow(smax_ptr, smax_val, &dst_reg->smax_value)) { dst_reg->smin_value = S64_MIN; dst_reg->smax_value = S64_MAX; - } else { - dst_reg->smin_value = smin_ptr + smin_val; - dst_reg->smax_value = smax_ptr + smax_val; } - if (umin_ptr + umin_val < umin_ptr || - umax_ptr + umax_val < umax_ptr) { + if (check_add_overflow(umin_ptr, umin_val, &dst_reg->umin_value) || + check_add_overflow(umax_ptr, umax_val, &dst_reg->umax_value)) { dst_reg->umin_value = 0; dst_reg->umax_value = U64_MAX; - } else { - dst_reg->umin_value = umin_ptr + umin_val; - dst_reg->umax_value = umax_ptr + umax_val; } dst_reg->var_off = tnum_add(ptr_reg->var_off, off_reg->var_off); dst_reg->off = ptr_reg->off; @@ -13363,21 +13337,15 @@ static void scalar32_min_max_add(struct bpf_reg_state *dst_reg, u32 umin_val = src_reg->u32_min_value; u32 umax_val = src_reg->u32_max_value; - if (signed_add32_overflows(dst_reg->s32_min_value, smin_val) || - signed_add32_overflows(dst_reg->s32_max_value, smax_val)) { + if (check_add_overflow(dst_reg->s32_min_value, smin_val, &dst_reg->s32_min_value) || + check_add_overflow(dst_reg->s32_max_value, smax_val, &dst_reg->s32_max_value)) { dst_reg->s32_min_value = S32_MIN; dst_reg->s32_max_value = S32_MAX; - } else { - dst_reg->s32_min_value += smin_val; - dst_reg->s32_max_value += smax_val; } - if (dst_reg->u32_min_value + umin_val < umin_val || - dst_reg->u32_max_value + umax_val < umax_val) { + if (check_add_overflow(dst_reg->u32_min_value, umin_val, &dst_reg->u32_min_value) || + check_add_overflow(dst_reg->u32_max_value, umax_val, &dst_reg->u32_max_value)) { dst_reg->u32_min_value = 0; dst_reg->u32_max_value = U32_MAX; - } else { - dst_reg->u32_min_value += umin_val; - dst_reg->u32_max_value += umax_val; } } @@ -13389,21 +13357,15 @@ static void scalar_min_max_add(struct bpf_reg_state *dst_reg, u64 umin_val = src_reg->umin_value; u64 umax_val = src_reg->umax_value; - if (signed_add_overflows(dst_reg->smin_value, smin_val) || - signed_add_overflows(dst_reg->smax_value, smax_val)) { + if (check_add_overflow(dst_reg->smin_value, smin_val, &dst_reg->smin_value) || + check_add_overflow(dst_reg->smax_value, smax_val, &dst_reg->smax_value)) { dst_reg->smin_value = S64_MIN; dst_reg->smax_value = S64_MAX; - } else { - dst_reg->smin_value += smin_val; - dst_reg->smax_value += smax_val; } - if (dst_reg->umin_value + umin_val < umin_val || - dst_reg->umax_value + umax_val < umax_val) { + if (check_add_overflow(dst_reg->umin_value, umin_val, &dst_reg->umin_value) || + check_add_overflow(dst_reg->umax_value, umax_val, &dst_reg->umax_value)) { dst_reg->umin_value = 0; dst_reg->umax_value = U64_MAX; - } else { - dst_reg->umin_value += umin_val; - dst_reg->umax_value += umax_val; } }