diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index 2ded1d2d..3d28a804 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -843,6 +843,41 @@ static int hart_mhpm_get_allowed_bits(void)
 	return num_bits;
 }
 
+struct hart_ext_validate_entry {
+	enum sbi_hart_extensions ext;
+	bool (*validate)(void);
+};
+
+static bool hart_ext_smepmp_validate(void)
+{
+	struct sbi_trap_info trap = {0};
+	unsigned long oldval;
+
+	oldval = csr_read_allowed(CSR_MSECCFG, &trap);
+	if (trap.cause)
+		return false;
+
+	csr_write_allowed(CSR_MSECCFG, &trap, oldval | MSECCFG_RLB);
+	if (trap.cause)
+		return false;
+
+	return (csr_swap(CSR_MSECCFG, oldval) & MSECCFG_RLB) == MSECCFG_RLB;
+}
+
+static const struct hart_ext_validate_entry hart_ext_validators[] = {
+	{ SBI_HART_EXT_SMEPMP, hart_ext_smepmp_validate },
+};
+
+static void hart_ext_validate(struct sbi_hart_features *hfeatures)
+{
+	for (int i = 0; i < (int)array_size(hart_ext_validators); i++) {
+		const struct hart_ext_validate_entry *v = &hart_ext_validators[i];
+
+		if (__test_bit(v->ext, hfeatures->extensions) && !v->validate())
+			__sbi_hart_update_extension(hfeatures, v->ext, false);
+	}
+}
+
 static int hart_detect_features(struct sbi_scratch *scratch)
 {
 	struct sbi_trap_info trap = {0};
@@ -1022,6 +1057,9 @@ static int hart_detect_features(struct sbi_scratch *scratch)
 	if (rc)
 		return rc;
 
+	/* Validate DT-claimed extensions against actual hardware */
+	hart_ext_validate(hfeatures);
+
 	/* Zicntr should only be detected using traps */
 	__sbi_hart_update_extension(hfeatures, SBI_HART_EXT_ZICNTR,
 			    sbi_hart_has_csr(scratch, SBI_HART_CSR_CYCLE) &&
diff --git a/lib/utils/fdt/fdt_fixup.c b/lib/utils/fdt/fdt_fixup.c
index ac75bfef..104153ae 100644
--- a/lib/utils/fdt/fdt_fixup.c
+++ b/lib/utils/fdt/fdt_fixup.c
@@ -11,6 +11,7 @@
 #include <libfdt.h>
 #include <sbi/riscv_asm.h>
 #include <sbi/sbi_console.h>
+#include <sbi/sbi_csr_detect.h>
 #include <sbi/sbi_domain.h>
 #include <sbi/sbi_math.h>
 #include <sbi/sbi_hart.h>
@@ -19,6 +20,7 @@
 #include <sbi/sbi_error.h>
 #include <sbi/sbi_heap.h>
 #include <sbi/sbi_timer.h>
+#include <sbi/sbi_trap.h>
 #include <sbi_utils/fdt/fdt_fixup.h>
 #include <sbi_utils/fdt/fdt_pmu.h>
 #include <sbi_utils/fdt/fdt_helper.h>
@@ -126,8 +128,29 @@ static bool isa_ext_zicbom_validate(void *fdt, int cpu_offset)
 	return fdt_parse_cbom_block_size(fdt, cpu_offset, &block_size) == 0;
 }
 
+static bool isa_ext_smepmp_validate(void *fdt, int cpu_offset)
+{
+	struct sbi_trap_info trap = {0};
+	unsigned long oldval;
+
+	(void)fdt;
+	(void)cpu_offset;
+
+	oldval = csr_read_allowed(CSR_MSECCFG, &trap);
+	if (trap.cause)
+		return false;
+
+	/* Probe Smepmp-specific RLB bit via write-readback */
+	csr_write_allowed(CSR_MSECCFG, &trap, oldval | MSECCFG_RLB);
+	if (trap.cause)
+		return false;
+
+	return (csr_swap(CSR_MSECCFG, oldval) & MSECCFG_RLB) == MSECCFG_RLB;
+}
+
 static const struct isa_ext_validate_entry isa_ext_validators[] = {
 	{ "h", isa_ext_h_validate },
+	{ "smepmp", isa_ext_smepmp_validate },
 	{ "zicbom", isa_ext_zicbom_validate },
 };