automatically mark immutable certain regions in program&ld.so LOADs.

The large commented block in elf_load_psection explains the sitaution.
ok kettenis.

2 files changed, 70 insertions, 13 deletions

diff --git a/sys/kern/exec_elf.c b/sys/kern/exec_elf.c
index a27dac2e817..8b5a67baea6 100644
--- a/sys/kern/exec_elf.c
+++ b/sys/kern/exec_elf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: exec_elf.c,v 1.168 2022/08/29 16:53:46 deraadt Exp $	*/
+/*	$OpenBSD: exec_elf.c,v 1.169 2022/10/21 18:10:56 deraadt Exp $	*/
 
 /*
  * Copyright (c) 1996 Per Fogelstrom
@@ -189,11 +189,18 @@ elf_load_psection(struct exec_vmcmd_set *vcset, struct vnode *vp,
 	 * initially.  The dynamic linker will make these read-only
 	 * and add back X permission after relocation processing.
 	 * Static executables with W|X segments will probably crash.
+	 * Apply immutability as much as possible, but not for RELRO
+	 * or PT_OPENBSD_MUTABLE sections, or LOADS marked
+	 * PF_OPENBSD_MUTABLE, or LOADS which violate W^X. Userland
+	 * (meaning crt0 or ld.so) will repair those regions.
 	 */
 	*prot |= (ph->p_flags & PF_R) ? PROT_READ : 0;
 	*prot |= (ph->p_flags & PF_W) ? PROT_WRITE : 0;
 	if ((ph->p_flags & PF_W) == 0)
 		*prot |= (ph->p_flags & PF_X) ? PROT_EXEC : 0;
+	if ((ph->p_flags & (PF_X | PF_W)) != (PF_X | PF_W) &&
+	    (ph->p_flags & PF_OPENBSD_MUTABLE) == 0)
+		flags |= VMCMD_IMMUTABLE;
 
 	msize = ph->p_memsz + diff;
 	offset = ph->p_offset - bdiff;
@@ -432,6 +439,12 @@ elf_load_file(struct proc *p, char *path, struct exec_package *epp,
 			    ph[i].p_memsz, ph[i].p_vaddr + pos, NULLVP, 0, 0);
 			break;
 
+		case PT_GNU_RELRO:
+		case PT_OPENBSD_MUTABLE:
+			NEW_VMCMD(&epp->ep_vmcmds, vmcmd_mutable,
+			    ph[i].p_memsz, ph[i].p_vaddr + pos, NULLVP, 0, 0);
+			break;
+
 		default:
 			break;
 		}
@@ -655,6 +668,12 @@ exec_elf_makecmds(struct proc *p, struct exec_package *epp)
 			    ph[i].p_memsz, ph[i].p_vaddr + exe_base, NULLVP, 0, 0);
 			break;
 
+		case PT_GNU_RELRO:
+		case PT_OPENBSD_MUTABLE:
+			NEW_VMCMD(&epp->ep_vmcmds, vmcmd_mutable,
+			    ph[i].p_memsz, ph[i].p_vaddr + exe_base, NULLVP, 0, 0);
+			break;
+
 		default:
 			/*
 			 * Not fatal, we don't need to understand everything
diff --git a/sys/kern/exec_subr.c b/sys/kern/exec_subr.c
index 8a949bebd28..dc4053a5f89 100644
--- a/sys/kern/exec_subr.c
+++ b/sys/kern/exec_subr.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: exec_subr.c,v 1.58 2022/10/07 14:59:39 deraadt Exp $	*/
+/*	$OpenBSD: exec_subr.c,v 1.59 2022/10/21 18:10:56 deraadt Exp $	*/
 /*	$NetBSD: exec_subr.c,v 1.9 1994/12/04 03:10:42 mycroft Exp $	*/
 
 /*
@@ -167,7 +167,7 @@ vmcmd_map_pagedvn(struct proc *p, struct exec_vmcmd *cmd)
 	 * call this routine.
 	 */
 	struct uvm_object *uobj;
-	unsigned int syscalls = 0;
+	unsigned int flags = UVM_FLAG_COPYONW | UVM_FLAG_FIXED;
 	int error;
 
 	/*
@@ -195,12 +195,12 @@ vmcmd_map_pagedvn(struct proc *p, struct exec_vmcmd *cmd)
 	 * do the map
 	 */
 	if ((cmd->ev_flags & VMCMD_SYSCALL) && (cmd->ev_prot & PROT_EXEC))
-		syscalls |= UVM_FLAG_SYSCALL;
+		flags |= UVM_FLAG_SYSCALL;
 
 	error = uvm_map(&p->p_vmspace->vm_map, &cmd->ev_addr, cmd->ev_len,
 	    uobj, cmd->ev_offset, 0,
 	    UVM_MAPFLAG(cmd->ev_prot, PROT_MASK, MAP_INHERIT_COPY,
-	    MADV_NORMAL, UVM_FLAG_COPYONW | UVM_FLAG_FIXED | syscalls));
+	    MADV_NORMAL, flags));
 
 	/*
 	 * check for error
@@ -211,6 +211,11 @@ vmcmd_map_pagedvn(struct proc *p, struct exec_vmcmd *cmd)
 		 * error: detach from object
 		 */
 		uobj->pgops->pgo_detach(uobj);
+	} else {
+		if (cmd->ev_flags & VMCMD_IMMUTABLE)
+			uvm_map_immutable(&p->p_vmspace->vm_map,
+			    cmd->ev_addr, round_page(cmd->ev_len),
+			    1, "pagedvn");
 	}
 
 	return (error);
@@ -234,7 +239,7 @@ vmcmd_map_readvn(struct proc *p, struct exec_vmcmd *cmd)
 
 	prot = cmd->ev_prot;
 
-	cmd->ev_addr = trunc_page(cmd->ev_addr); /* required by uvm_map */
+	KASSERT((cmd->ev_addr & PAGE_MASK) == 0);
 	error = uvm_map(&p->p_vmspace->vm_map, &cmd->ev_addr,
 	    round_page(cmd->ev_len), NULL, UVM_UNKNOWN_OFFSET, 0,
 	    UVM_MAPFLAG(prot | PROT_WRITE, PROT_MASK, MAP_INHERIT_COPY,
@@ -256,12 +261,19 @@ vmcmd_map_readvn(struct proc *p, struct exec_vmcmd *cmd)
 		 * it mapped read-only, so now we are going to have to call
 		 * uvm_map_protect() to fix up the protection.  ICK.
 		 */
-		return (uvm_map_protect(&p->p_vmspace->vm_map,
-		    trunc_page(cmd->ev_addr),
-		    round_page(cmd->ev_addr + cmd->ev_len),
+		error = (uvm_map_protect(&p->p_vmspace->vm_map,
+		    cmd->ev_addr, round_page(cmd->ev_len),
 		    prot, FALSE, TRUE));
 	}
-	return (0);
+	if (error == 0) {
+		if (cmd->ev_flags & VMCMD_IMMUTABLE) {
+			//printf("imut readvn\n");
+			uvm_map_immutable(&p->p_vmspace->vm_map,
+			    cmd->ev_addr, round_page(cmd->ev_len),
+			    1, "readvn");
+		}
+	}
+	return (error);
 }
 
 /*
@@ -272,15 +284,41 @@ vmcmd_map_readvn(struct proc *p, struct exec_vmcmd *cmd)
 int
 vmcmd_map_zero(struct proc *p, struct exec_vmcmd *cmd)
 {
+	int error;
+
 	if (cmd->ev_len == 0)
 		return (0);
 	
-	cmd->ev_addr = trunc_page(cmd->ev_addr); /* required by uvm_map */
-	return (uvm_map(&p->p_vmspace->vm_map, &cmd->ev_addr,
+	KASSERT((cmd->ev_addr & PAGE_MASK) == 0);
+	error = uvm_map(&p->p_vmspace->vm_map, &cmd->ev_addr,
 	    round_page(cmd->ev_len), NULL, UVM_UNKNOWN_OFFSET, 0,
 	    UVM_MAPFLAG(cmd->ev_prot, PROT_MASK, MAP_INHERIT_COPY,
 	    MADV_NORMAL, UVM_FLAG_FIXED|UVM_FLAG_COPYONW |
-	    (cmd->ev_flags & VMCMD_STACK ? UVM_FLAG_STACK : 0))));
+	    (cmd->ev_flags & VMCMD_STACK ? UVM_FLAG_STACK : 0)));
+	if (cmd->ev_flags & VMCMD_IMMUTABLE) {
+		//printf("imut zero\n");
+		uvm_map_immutable(&p->p_vmspace->vm_map,
+		    cmd->ev_addr, round_page(cmd->ev_len),
+		    1, "zero");
+	}
+	return error;
+}
+
+/*
+ * vmcmd_mutable():
+ *	handle vmcmd which changes an address space region.back to mutable
+ */
+
+int
+vmcmd_mutable(struct proc *p, struct exec_vmcmd *cmd)
+{
+	if (cmd->ev_len == 0)
+		return (0);
+	
+	/* ev_addr, ev_len may be misaligned, so maximize the region */
+	uvm_map_immutable(&p->p_vmspace->vm_map, trunc_page(cmd->ev_addr),
+	    round_page(cmd->ev_addr + cmd->ev_len), 0, "mutable");
+	return 0;
 }
 
 /*