x86/dumpstack: Don't dump kernel memory based on usermode RIP

commit 342db04ae71273322f0011384a9ed414df8bdae4 upstream.

show_opcodes() is used both for dumping kernel instructions and for dumping
user instructions. If userspace causes #PF by jumping to a kernel address,
show_opcodes() can be reached with regs->ip controlled by the user,
pointing to kernel code. Make sure that userspace can't trick us into
dumping kernel memory into dmesg.

Fixes: 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: security@kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180828154901.112726-1-jannh@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index b6dc698f992a54646266ba7a4dc2901e7bdfa109..f335aad404a479e98e4a5d38dc41ee5e5aa419ec 100644 (file)
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
        return (unsigned long)frame;
 }
 
-void show_opcodes(u8 *rip, const char *loglvl);
+void show_opcodes(struct pt_regs *regs, const char *loglvl);
 void show_ip(struct pt_regs *regs, const char *loglvl);
 #endif /* _ASM_X86_STACKTRACE_H */

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 48b660cb84f46ef915aeb1ecf8f9b2ff31120517..17b02adc79aa579a5d872402e76a21a2cbaf2700 100644 (file)
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -92,23 +92,32 @@ static void printk_stack_address(unsigned long address, int reliable,
  * Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
  * guesstimate in attempt to achieve all of the above.
  */
-void show_opcodes(u8 *rip, const char *loglvl)
+void show_opcodes(struct pt_regs *regs, const char *loglvl)
 {
        unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3;
        u8 opcodes[OPCODE_BUFSIZE];
-       u8 *ip;
+       unsigned long ip;
        int i;
+       bool bad_ip;
 
        printk("%sCode: ", loglvl);
 
-       ip = (u8 *)rip - code_prologue;
-       if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
+       ip = regs->ip - code_prologue;
+
+       /*
+        * Make sure userspace isn't trying to trick us into dumping kernel
+        * memory by pointing the userspace instruction pointer at it.
+        */
+       bad_ip = user_mode(regs) &&
+                __chk_range_not_ok(ip, OPCODE_BUFSIZE, TASK_SIZE_MAX);
+
+       if (bad_ip || probe_kernel_read(opcodes, (u8 *)ip, OPCODE_BUFSIZE)) {
                pr_cont("Bad RIP value.\n");
                return;
        }
 
        for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) {
-               if (ip == rip)
+               if (ip == regs->ip)
                        pr_cont("<%02x> ", opcodes[i]);
                else
                        pr_cont("%02x ", opcodes[i]);
@@ -123,7 +132,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
 #else
        printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
 #endif
-       show_opcodes((u8 *)regs->ip, loglvl);
+       show_opcodes(regs, loglvl);
 }
 
 void show_iret_regs(struct pt_regs *regs)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 2aafa6ab6103d150ad26e097221a972f5d16363f..d1f1612672c7e927e8db07cf0b050b17539a5ff4 100644 (file)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -838,7 +838,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
 
        printk(KERN_CONT "\n");
 
-       show_opcodes((u8 *)regs->ip, loglvl);
+       show_opcodes(regs, loglvl);
 }
 
 static void