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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: 7cccf0725c ("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
This commit is contained in:
Jann Horn 2018-08-28 17:49:01 +02:00 committed by Thomas Gleixner
parent 26e609eccd
commit 342db04ae7
3 changed files with 15 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/stacktrace.h
View File

@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
return (unsigned long)frame; 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); void show_ip(struct pt_regs *regs, const char *loglvl);
#endif /* _ASM_X86_STACKTRACE_H */ #endif /* _ASM_X86_STACKTRACE_H */

16
arch/x86/kernel/dumpstack.c
View File

@ -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 * Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
* guesstimate in attempt to achieve all of the above. * 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 PROLOGUE_SIZE 42
#define EPILOGUE_SIZE 21 #define EPILOGUE_SIZE 21
#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE) #define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
u8 opcodes[OPCODE_BUFSIZE]; 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); printk("%sCode: Bad RIP value.\n", loglvl);
} else { } else {
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %" printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
@ -113,7 +123,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
#else #else
printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip); printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
#endif #endif
show_opcodes((u8 *)regs->ip, loglvl); show_opcodes(regs, loglvl);
} }
void show_iret_regs(struct pt_regs *regs) void show_iret_regs(struct pt_regs *regs)

2
arch/x86/mm/fault.c
View File

@ -837,7 +837,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
printk(KERN_CONT "\n"); printk(KERN_CONT "\n");
show_opcodes((u8 *)regs->ip, loglvl); show_opcodes(regs, loglvl);
} }
static void static void