RISC-V: Check that the DTB doesn't overlap with kernel

This can happen with very large kernels (e.g. ones embedding a root
filesystem). The DTB written by OpenSBI/BBL is quite small so this is
unlikely to hit important data, but if it does this can result in very
confusing and hard-to-debug crashes. Add a KASSERT() and a verbose print
to catch this problem with debug kernels.

While this will not print any output by default if it fails (that would
depend on EARLY_PRINTF), at least the kernel now halts reliably instead
of randomly crashing.

Reviewed By:	mhorne
Differential Revision: https://reviews.freebsd.org/D25153

sys/riscv/include/machdep.h

@@ -42,6 +42,7 @@ struct riscv_bootparams {
 	vm_offset_t	kern_phys;	/* Kernel base (physical) addr */
 	vm_offset_t	kern_stack;
 	vm_offset_t	dtbp_virt;	/* Device tree blob virtual addr */
+	vm_offset_t	dtbp_phys;	/* Device tree blob physical addr */
 };
 
 extern vm_paddr_t physmap[PHYS_AVAIL_ENTRIES];

sys/riscv/riscv/genassym.c

@@ -106,3 +106,4 @@ ASSYM(RISCV_BOOTPARAMS_KERN_PHYS, offsetof(struct riscv_bootparams, kern_phys));
 ASSYM(RISCV_BOOTPARAMS_KERN_STACK, offsetof(struct riscv_bootparams,
     kern_stack));
 ASSYM(RISCV_BOOTPARAMS_DTBP_VIRT, offsetof(struct riscv_bootparams, dtbp_virt));
+ASSYM(RISCV_BOOTPARAMS_DTBP_PHYS, offsetof(struct riscv_bootparams, dtbp_phys));

sys/riscv/riscv/locore.S

@@ -221,6 +221,7 @@ va:
 	and	t1, a1, t1
 	add	t0, t0, t1
 	sd	t0, RISCV_BOOTPARAMS_DTBP_VIRT(sp)
+	sd	a1, RISCV_BOOTPARAMS_DTBP_PHYS(sp)
 
 	mv	a0, sp
 	call	_C_LABEL(initriscv)	/* Off we go */

sys/riscv/riscv/machdep.c

@@ -776,9 +776,20 @@ fake_preload_metadata(struct riscv_bootparams *rvbp)
 	PRELOAD_PUSH_VALUE(uint32_t, 0);
 	preload_metadata = (caddr_t)fake_preload;
 
+	/* Check if bootloader clobbered part of the kernel with the DTB. */
+	KASSERT(rvbp->dtbp_phys + dtb_size <= rvbp->kern_phys ||
+		rvbp->dtbp_phys >= rvbp->kern_phys + (lastaddr - KERNBASE),
+	    ("FDT (%lx-%lx) and kernel (%lx-%lx) overlap", rvbp->dtbp_phys,
+		rvbp->dtbp_phys + dtb_size, rvbp->kern_phys,
+		rvbp->kern_phys + (lastaddr - KERNBASE)));
 	KASSERT(fake_size < sizeof(fake_preload),
 	    ("Too many fake_preload items"));
 
+	if (boothowto & RB_VERBOSE)
+		printf("FDT phys (%lx-%lx), kernel phys (%lx-%lx)\n",
+		    rvbp->dtbp_phys, rvbp->dtbp_phys + dtb_size,
+		    rvbp->kern_phys, rvbp->kern_phys + (lastaddr - KERNBASE));
+
 	return (lastaddr);
 }