linux-kernel - [PATCH 06/44] bpf: Verifier, remove some unusual uses of min_t() and max

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Message-Id: <20251119224140.8616-7-david.laight.linux@gmail.com>
Date: Wed, 19 Nov 2025 22:41:02 +0000
From: david.laight.linux@...il.com
To: linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Laight <david.laight.linux@...il.com>
Subject: [PATCH 06/44] bpf: Verifier, remove some unusual uses of min_t() and max_t()

From: David Laight <david.laight.linux@...il.com>

min_t() and max_t() are normally used to change the signedness
of a positive value to avoid a signed-v-unsigned compare warning.

However they are used here to convert an unsigned 64bit pattern
to a signed to a 32/64bit signed number.
To avoid any confusion use plain min()/max() and explicitely cast
the u64 expression to the correct signed value.

Use a simple max() for the max_pkt_offset calulation and delete the
comment about why the cast to u32 is safe.

Signed-off-by: David Laight <david.laight.linux@...il.com>
---
 kernel/bpf/verifier.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ff40e5e65c43..22fa9769fbdb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2319,12 +2319,12 @@ static void __update_reg32_bounds(struct bpf_reg_state *reg)
 	struct tnum var32_off = tnum_subreg(reg->var_off);
 
 	/* min signed is max(sign bit) | min(other bits) */
-	reg->s32_min_value = max_t(s32, reg->s32_min_value,
-			var32_off.value | (var32_off.mask & S32_MIN));
+	reg->s32_min_value = max(reg->s32_min_value,
+			(s32)(var32_off.value | (var32_off.mask & S32_MIN)));
 	/* max signed is min(sign bit) | max(other bits) */
-	reg->s32_max_value = min_t(s32, reg->s32_max_value,
-			var32_off.value | (var32_off.mask & S32_MAX));
-	reg->u32_min_value = max_t(u32, reg->u32_min_value, (u32)var32_off.value);
+	reg->s32_max_value = min(reg->s32_max_value,
+			(s32)(var32_off.value | (var32_off.mask & S32_MAX)));
+	reg->u32_min_value = max(reg->u32_min_value, (u32)var32_off.value);
 	reg->u32_max_value = min(reg->u32_max_value,
 				 (u32)(var32_off.value | var32_off.mask));
 }
@@ -2332,11 +2332,11 @@ static void __update_reg32_bounds(struct bpf_reg_state *reg)
 static void __update_reg64_bounds(struct bpf_reg_state *reg)
 {
 	/* min signed is max(sign bit) | min(other bits) */
-	reg->smin_value = max_t(s64, reg->smin_value,
-				reg->var_off.value | (reg->var_off.mask & S64_MIN));
+	reg->smin_value = max(reg->smin_value,
+				(s64)(reg->var_off.value | (reg->var_off.mask & S64_MIN)));
 	/* max signed is min(sign bit) | max(other bits) */
-	reg->smax_value = min_t(s64, reg->smax_value,
-				reg->var_off.value | (reg->var_off.mask & S64_MAX));
+	reg->smax_value = min(reg->smax_value,
+				(s64)(reg->var_off.value | (reg->var_off.mask & S64_MAX)));
 	reg->umin_value = max(reg->umin_value, reg->var_off.value);
 	reg->umax_value = min(reg->umax_value,
 			      reg->var_off.value | reg->var_off.mask);
@@ -6128,15 +6128,8 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off,
 		return err;
 	}
 
-	/* __check_mem_access has made sure "off + size - 1" is within u16.
-	 * reg->umax_value can't be bigger than MAX_PACKET_OFF which is 0xffff,
-	 * otherwise find_good_pkt_pointers would have refused to set range info
-	 * that __check_mem_access would have rejected this pkt access.
-	 * Therefore, "off + reg->umax_value + size - 1" won't overflow u32.
-	 */
-	env->prog->aux->max_pkt_offset =
-		max_t(u32, env->prog->aux->max_pkt_offset,
-		      off + reg->umax_value + size - 1);
+	env->prog->aux->max_pkt_offset = max(env->prog->aux->max_pkt_offset,
+					     off + reg->umax_value + size - 1);
 
 	return err;
 }
-- 
2.39.5