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
......@@ -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 */
......@@ -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)
......
......@@ -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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