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Commit fd11a649 authored by Ricardo Neri's avatar Ricardo Neri Committed by Ingo Molnar
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x86/umip: Print a warning into the syslog if UMIP-protected instructions are used 



Print a rate-limited warning when a user-space program attempts to execute
any of the instructions that UMIP protects (i.e., SGDT, SIDT, SLDT, STR
and SMSW).

This is useful, because when CONFIG_X86_INTEL_UMIP=y is selected and
supported by the hardware, user space programs that try to execute such
instructions will receive a SIGSEGV signal that they might not expect.

In the specific cases for which emulation is provided (instructions SGDT,
SIDT and SMSW in protected and virtual-8086 modes), no signal is
generated. However, a warning is helpful to encourage updates in such
programs to avoid the use of such instructions.

Warnings are printed via a customized printk() function that also provides
information about the program that attempted to use the affected
instructions.

Utility macros are defined to wrap umip_printk() for the error and warning
kernel log levels.

While here, replace an existing call to the generic rate-limited pr_err()
with the new umip_pr_err().

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarRicardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: ricardo.neri@intel.com
Link: http://lkml.kernel.org/r/1511233476-17088-1-git-send-email-ricardo.neri-calderon@linux.intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent b4c0a732

arch/x86/kernel/umip.c

+58 −4
Original line number Diff line number Diff line
@@ -82,6 +82,57 @@ 
#define	UMIP_INST_SLDT  3       /* 0F 00 /0 */

#define	UMIP_INST_STR   4       /* 0F 00 /1 */



const char * const umip_insns[5] = {

	[UMIP_INST_SGDT] = "SGDT",

	[UMIP_INST_SIDT] = "SIDT",

	[UMIP_INST_SMSW] = "SMSW",

	[UMIP_INST_SLDT] = "SLDT",

	[UMIP_INST_STR] = "STR",

};



#define umip_pr_err(regs, fmt, ...) \

	umip_printk(regs, KERN_ERR, fmt, ##__VA_ARGS__)

#define umip_pr_warning(regs, fmt, ...) \

	umip_printk(regs, KERN_WARNING, fmt,  ##__VA_ARGS__)



/**

 * umip_printk() - Print a rate-limited message

 * @regs:	Register set with the context in which the warning is printed

 * @log_level:	Kernel log level to print the message

 * @fmt:	The text string to print

 *

 * Print the text contained in @fmt. The print rate is limited to bursts of 5

 * messages every two minutes. The purpose of this customized version of

 * printk() is to print messages when user space processes use any of the

 * UMIP-protected instructions. Thus, the printed text is prepended with the

 * task name and process ID number of the current task as well as the

 * instruction and stack pointers in @regs as seen when entering kernel mode.

 *

 * Returns:

 *

 * None.

 */

static __printf(3, 4)

void umip_printk(const struct pt_regs *regs, const char *log_level,

		 const char *fmt, ...)

{

	/* Bursts of 5 messages every two minutes */

	static DEFINE_RATELIMIT_STATE(ratelimit, 2 * 60 * HZ, 5);

	struct task_struct *tsk = current;

	struct va_format vaf;

	va_list args;



	if (!__ratelimit(&ratelimit))

		return;



	va_start(args, fmt);

	vaf.fmt = fmt;

	vaf.va = &args;

	printk("%s" pr_fmt("%s[%d] ip:%lx sp:%lx: %pV"), log_level, tsk->comm,

	       task_pid_nr(tsk), regs->ip, regs->sp, &vaf);

	va_end(args);

}



/**

 * identify_insn() - Identify a UMIP-protected instruction

 * @insn:	Instruction structure with opcode and ModRM byte.
@@ -236,10 +287,8 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs) 
	if (!(show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)))

		return;



	pr_err_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%x in %lx\n",

			   tsk->comm, task_pid_nr(tsk), regs->ip,

			   regs->sp, X86_PF_USER | X86_PF_WRITE,

			   regs->ip);

	umip_pr_err(regs, "segfault in emulation. error%x\n",

		    X86_PF_USER | X86_PF_WRITE);

}



/**
@@ -326,10 +375,15 @@ bool fixup_umip_exception(struct pt_regs *regs) 
	if (umip_inst < 0)

		return false;



	umip_pr_warning(regs, "%s instruction cannot be used by applications.\n",

			umip_insns[umip_inst]);



	/* Do not emulate SLDT, STR or user long mode processes. */

	if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))

		return false;



	umip_pr_warning(regs, "For now, expensive software emulation returns the result.\n");



	if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))

		return false;