4.18-stable review patch. If anyone has any objections, please let me know.
------------------ From: Jann Horn <[email protected]> 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 <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Reviewed-by: Kees Cook <[email protected]> Reviewed-by: Borislav Petkov <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: [email protected] Cc: [email protected] Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Greg Kroah-Hartman <[email protected]> --- arch/x86/include/asm/stacktrace.h | 2 +- arch/x86/kernel/dumpstack.c | 21 +++++++++++++++------ arch/x86/mm/fault.c | 2 +- 3 files changed, 17 insertions(+), 8 deletions(-) --- a/arch/x86/include/asm/stacktrace.h +++ b/arch/x86/include/asm/stacktrace.h @@ -111,6 +111,6 @@ static inline unsigned long caller_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); #endif /* _ASM_X86_STACKTRACE_H */ --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -92,23 +92,32 @@ static void printk_stack_address(unsigne * 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 #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) --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -838,7 +838,7 @@ show_signal_msg(struct pt_regs *regs, un printk(KERN_CONT "\n"); - show_opcodes((u8 *)regs->ip, loglvl); + show_opcodes(regs, loglvl); } static void
