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Date:      Wed, 6 May 2020 17:12:26 +0000 (UTC)
From:      Brooks Davis <brooks@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org
Subject:   svn commit: r360693 - stable/12/sys/mips/mips
Message-ID:  <202005061712.046HCQkw048688@repo.freebsd.org>
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Author: brooks
Date: Wed May  6 17:12:26 2020
New Revision: 360693
URL: https://svnweb.freebsd.org/changeset/base/360693

Log:
  MFC r359974:
  
  Don't directly access userspace memory.
  
  Rather then using the racy useracc() followed by direct access to
  userspace memory, perform a copyin() and use the result if it succeeds.
  
  Reviewed by:	jhb
  Sponsored by:	DARPA
  Differential Revision:	https://reviews.freebsd.org/D24410

Modified:
  stable/12/sys/mips/mips/trap.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/mips/mips/trap.c
==============================================================================
--- stable/12/sys/mips/mips/trap.c	Wed May  6 15:24:31 2020	(r360692)
+++ stable/12/sys/mips/mips/trap.c	Wed May  6 17:12:26 2020	(r360693)
@@ -1404,7 +1404,7 @@ log_illegal_instruction(const char *msg, struct trapfr
 {
 	pt_entry_t *ptep;
 	pd_entry_t *pdep;
-	unsigned int *addr;
+	unsigned int *addr, instr[4];
 	struct thread *td;
 	struct proc *p;
 	register_t pc;
@@ -1431,17 +1431,16 @@ log_illegal_instruction(const char *msg, struct trapfr
 	 * Dump a few words around faulting instruction, if the addres is
 	 * valid.
 	 */
-	if (!(pc & 3) &&
-	    useracc((caddr_t)(intptr_t)pc, sizeof(int) * 4, VM_PROT_READ)) {
+	addr = (unsigned int *)(intptr_t)pc;
+	if ((pc & 3) == 0 && copyin(addr, instr, sizeof(instr)) == 0) {
 		/* dump page table entry for faulting instruction */
 		log(LOG_ERR, "Page table info for pc address %#jx: pde = %p, pte = %#jx\n",
 		    (intmax_t)pc, (void *)(intptr_t)*pdep, (uintmax_t)(ptep ? *ptep : 0));
 
-		addr = (unsigned int *)(intptr_t)pc;
 		log(LOG_ERR, "Dumping 4 words starting at pc address %p: \n",
 		    addr);
 		log(LOG_ERR, "%08x %08x %08x %08x\n",
-		    addr[0], addr[1], addr[2], addr[3]);
+		    instr[0], instr[1], instr[2], instr[3]);
 	} else {
 		log(LOG_ERR, "pc address %#jx is inaccessible, pde = %p, pte = %#jx\n",
 		    (intmax_t)pc, (void *)(intptr_t)*pdep, (uintmax_t)(ptep ? *ptep : 0));
@@ -1453,7 +1452,7 @@ log_bad_page_fault(char *msg, struct trapframe *frame,
 {
 	pt_entry_t *ptep;
 	pd_entry_t *pdep;
-	unsigned int *addr;
+	unsigned int *addr, instr[4];
 	struct thread *td;
 	struct proc *p;
 	char *read_or_write;
@@ -1501,18 +1500,18 @@ log_bad_page_fault(char *msg, struct trapframe *frame,
 	 * Dump a few words around faulting instruction, if the addres is
 	 * valid.
 	 */
-	if (!(pc & 3) && (pc != frame->badvaddr) &&
-	    (trap_type != T_BUS_ERR_IFETCH) &&
-	    useracc((caddr_t)(intptr_t)pc, sizeof(int) * 4, VM_PROT_READ)) {
+	addr = (unsigned int *)(intptr_t)pc;
+	if ((pc & 3) == 0 && pc != frame->badvaddr &&
+	    trap_type != T_BUS_ERR_IFETCH &&
+	    copyin((caddr_t)(intptr_t)pc, instr, sizeof(instr)) == 0) {
 		/* dump page table entry for faulting instruction */
 		log(LOG_ERR, "Page table info for pc address %#jx: pde = %p, pte = %#jx\n",
 		    (intmax_t)pc, (void *)(intptr_t)*pdep, (uintmax_t)(ptep ? *ptep : 0));
 
-		addr = (unsigned int *)(intptr_t)pc;
 		log(LOG_ERR, "Dumping 4 words starting at pc address %p: \n",
 		    addr);
 		log(LOG_ERR, "%08x %08x %08x %08x\n",
-		    addr[0], addr[1], addr[2], addr[3]);
+		    instr[0], instr[1], instr[2], instr[3]);
 	} else {
 		log(LOG_ERR, "pc address %#jx is inaccessible, pde = %p, pte = %#jx\n",
 		    (intmax_t)pc, (void *)(intptr_t)*pdep, (uintmax_t)(ptep ? *ptep : 0));

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