Commit 342db04a authored by Jann Horn's avatar Jann Horn Committed by Thomas Gleixner
Browse files

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




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: 7cccf072 ("x86/dumpstack: Add a show_ip() function")
Signed-off-by: default avatarJann Horn <jannh@google.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarBorislav 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
parent 26e609ec

arch/x86/include/asm/stacktrace.h

+1 −1
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/dumpstack.c

+13 −3
Original line number Diff line number Diff line
@@ -90,14 +90,24 @@ 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)

{

#define PROLOGUE_SIZE 42

#define EPILOGUE_SIZE 21

#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)

	u8 opcodes[OPCODE_BUFSIZE];

	unsigned long prologue = regs->ip - PROLOGUE_SIZE;

	bool bad_ip;



	if (probe_kernel_read(opcodes, rip - PROLOGUE_SIZE, OPCODE_BUFSIZE)) {

	/*

	 * 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(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);



	if (bad_ip || probe_kernel_read(opcodes, (u8 *)prologue,

					OPCODE_BUFSIZE)) {

		printk("%sCode: Bad RIP value.\n", loglvl);

	} else {

		printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
@@ -113,7 +123,7 @@ 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)

arch/x86/mm/fault.c

+1 −1
Original line number Diff line number Diff line
@@ -837,7 +837,7 @@ 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

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