git: 4a9f2f8b07c2 - main - riscv: handle page faults in the unmappable region

The branch main has been updated by mhorne:

URL: https://cgit.FreeBSD.org/src/commit/?id=4a9f2f8b07c2d1a1c12f4aabdccd36f56b20cfda

commit 4a9f2f8b07c2d1a1c12f4aabdccd36f56b20cfda
Author:     Mitchell Horne <mhorne@FreeBSD.org>
AuthorDate: 2021-10-07 21:05:38 +0000
Commit:     Mitchell Horne <mhorne@FreeBSD.org>
CommitDate: 2021-10-07 21:12:17 +0000

    riscv: handle page faults in the unmappable region
    
    When handling a kernel page fault, check explicitly that stval resides
    in either the user or kernel address spaces, and make the page fault
    fatal if not. Otherwise, a properly crafted address may appear to
    pmap_fault() as a valid and present page in the kernel map, causing the
    page fault to be retried continuously. This is mainly due to the fact
    that the upper bits of virtual addresses are not validated by most of
    the pmap code.
    
    Faults of this nature should only occur due to some kind of bug in the
    kernel, but it is best to handle them gracefully when they do.
    
    Handle user page faults in the same way, sending a SIGSEGV immediately
    when a malformed address is encountered.
    
    Add an assertion to pmap_l1(), which should help catch other bugs of
    this kind that make it this far.
    
    Reviewed by:    jrtc27, markj
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D31208
---
 sys/riscv/include/vmparam.h | 4 ++++
 sys/riscv/riscv/pmap.c      | 2 ++
 sys/riscv/riscv/trap.c      | 8 ++++++++
 3 files changed, 14 insertions(+)

diff --git a/sys/riscv/include/vmparam.h b/sys/riscv/include/vmparam.h
index 94782da779f7..4ed95def2caa 100644
--- a/sys/riscv/include/vmparam.h
+++ b/sys/riscv/include/vmparam.h
@@ -186,6 +186,10 @@
 #define	VM_MINUSER_ADDRESS	(VM_MIN_USER_ADDRESS)
 #define	VM_MAXUSER_ADDRESS	(VM_MAX_USER_ADDRESS)
 
+/* Check if an address resides in a mappable region. */
+#define	VIRT_IS_VALID(va)						\
+    (((va) < VM_MAX_USER_ADDRESS) || ((va) >= VM_MIN_KERNEL_ADDRESS))
+
 #define	KERNBASE		(VM_MIN_KERNEL_ADDRESS)
 #define	SHAREDPAGE		(VM_MAXUSER_ADDRESS - PAGE_SIZE)
 #define	USRSTACK		SHAREDPAGE
diff --git a/sys/riscv/riscv/pmap.c b/sys/riscv/riscv/pmap.c
index df80f07df0ca..0918325c13fb 100644
--- a/sys/riscv/riscv/pmap.c
+++ b/sys/riscv/riscv/pmap.c
@@ -351,6 +351,8 @@ static __inline pd_entry_t *
 pmap_l1(pmap_t pmap, vm_offset_t va)
 {
 
+	KASSERT(VIRT_IS_VALID(va),
+	    ("%s: malformed virtual address %#lx", __func__, va));
 	return (&pmap->pm_l1[pmap_l1_index(va)]);
 }
 
diff --git a/sys/riscv/riscv/trap.c b/sys/riscv/riscv/trap.c
index 8844638c8204..8eb52fcc5337 100644
--- a/sys/riscv/riscv/trap.c
+++ b/sys/riscv/riscv/trap.c
@@ -200,6 +200,11 @@ page_fault_handler(struct trapframe *frame, int usermode)
 		goto fatal;
 
 	if (usermode) {
+		if (!VIRT_IS_VALID(stval)) {
+			call_trapsignal(td, SIGSEGV, SEGV_MAPERR, (void *)stval,
+			    frame->tf_scause & SCAUSE_CODE);
+			goto done;
+		}
 		map = &td->td_proc->p_vmspace->vm_map;
 	} else {
 		/*
@@ -208,6 +213,9 @@ page_fault_handler(struct trapframe *frame, int usermode)
 		 */
 		intr_enable();
 
+		if (!VIRT_IS_VALID(stval))
+			goto fatal;
+
 		if (stval >= VM_MAX_USER_ADDRESS) {
 			map = kernel_map;
 		} else {