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Subject[tip:x86/urgent] x86/umip: Print a warning into the syslog if UMIP-protected instructions are used
Commit-ID:  fd11a6496e12848d4eeb21029c2c288bbc638048
Gitweb: https://git.kernel.org/tip/fd11a6496e12848d4eeb21029c2c288bbc638048
Author: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
AuthorDate: Mon, 20 Nov 2017 19:04:36 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 21 Nov 2017 08:13:43 +0100

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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Thomas 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: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/umip.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 58 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 1f1f2d5..dabbac3 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -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;

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