Merge branch 'fix-truncation-bug-in-coerce_reg_to_size_sx-and-extend-selftests'

Dimitar Kanaliev says:

====================
Fix truncation bug in coerce_reg_to_size_sx and extend selftests.

This patch series addresses a truncation bug in the eBPF verifier function
coerce_reg_to_size_sx(). The issue was caused by the incorrect ordering
of assignments between 32-bit and 64-bit min/max values, leading to
improper truncation when updating the register state. This issue has been
reported previously by Zac Ecob[1] , but was not followed up on.

The first patch fixes the assignment order in coerce_reg_to_size_sx()
to ensure correct truncation. The subsequent patches add selftests for
coerce_{reg,subreg}_to_size_sx.

Changelog:
	v1 -> v2:
	 - Moved selftests inside the conditional check for cpuv4

[1] (https://lore.kernel.org/bpf/h3qKLDEO6m9nhif0eAQX4fVrqdO0D_OPb0y5HfMK9jBePEKK33wQ3K-bqSVnr0hiZdFZtSJOsbNkcEQGpv_yJk61PAAiO8fUkgMRSO-lB50=@protonmail.com/)
====================

Link: https://lore.kernel.org/r/20241014121155.92887-1-dimitar.kanaliev@siteground.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

kernel/bpf/verifier.c

@@ -6339,10 +6339,10 @@ static void coerce_reg_to_size_sx(struct bpf_reg_state *reg, int size)
 
 	/* both of s64_max/s64_min positive or negative */
 	if ((s64_max >= 0) == (s64_min >= 0)) {
-		reg->smin_value = reg->s32_min_value = s64_min;
-		reg->smax_value = reg->s32_max_value = s64_max;
-		reg->umin_value = reg->u32_min_value = s64_min;
-		reg->umax_value = reg->u32_max_value = s64_max;
+		reg->s32_min_value = reg->smin_value = s64_min;
+		reg->s32_max_value = reg->smax_value = s64_max;
+		reg->u32_min_value = reg->umin_value = s64_min;
+		reg->u32_max_value = reg->umax_value = s64_max;
 		reg->var_off = tnum_range(s64_min, s64_max);
 		return;
 	}

tools/testing/selftests/bpf/progs/verifier_movsx.c

@@ -287,6 +287,46 @@ l0_%=:							\
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("MOV64SX, S8, unsigned range_check")
+__success __retval(0)
+__naked void mov64sx_s8_range_check(void)
+{
+	asm volatile ("					\
+	call %[bpf_get_prandom_u32];			\
+	r0 &= 0x1;					\
+	r0 += 0xfe;					\
+	r0 = (s8)r0;					\
+	if r0 < 0xfffffffffffffffe goto label_%=;	\
+	r0 = 0;						\
+	exit;						\
+label_%=:						\
+	exit;						\
+"	:
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("MOV32SX, S8, unsigned range_check")
+__success __retval(0)
+__naked void mov32sx_s8_range_check(void)
+{
+	asm volatile ("                                 \
+	call %[bpf_get_prandom_u32];                    \
+	w0 &= 0x1;                                      \
+	w0 += 0xfe;                                     \
+	w0 = (s8)w0;                                    \
+	if w0 < 0xfffffffe goto label_%=;               \
+	r0 = 0;                                         \
+	exit;                                           \
+label_%=: 	                                        \
+	exit;                                           \
+	"      :
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
 #else
 
 SEC("socket")