Re: [PATCH v15 04/26] x86/cet: Add control-protection fault handler
From: Borislav Petkov <bp@alien8.de>
Date: 2020-11-26 18:49:43
Also in:
linux-arch, linux-doc, linux-mm, lkml
On Tue, Nov 10, 2020 at 08:21:49AM -0800, Yu-cheng Yu wrote:
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index e19df6cde35d..6c21c1e92605 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c@@ -598,6 +598,65 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection) cond_local_irq_disable(regs); } +#ifdef CONFIG_X86_CET +static const char * const control_protection_err[] = { + "unknown", + "near-ret", + "far-ret/iret", + "endbranch", + "rstorssp", + "setssbsy", +}; + +/* + * When a control protection exception occurs, send a signal + * to the responsible application. Currently, control + * protection is only enabled for the user mode. This + * exception should not come from the kernel mode. + */
Make that 80 cols wide.
quoted hunk ↗ jump to hunk
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection) +{ + struct task_struct *tsk; + + if (notify_die(DIE_TRAP, "control protection fault", regs, + error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP) + return;
What is the intent here, notifiers can prevent the machine from printing the CP error below?
quoted hunk ↗ jump to hunk
+ cond_local_irq_enable(regs); + + if (!user_mode(regs)) + die("kernel control protection fault", regs, error_code);
Let's write that more explicitly:
die("Unexpected/unsupported control protection fault"...
quoted hunk ↗ jump to hunk
+ + if (!static_cpu_has(X86_FEATURE_SHSTK) && + !static_cpu_has(X86_FEATURE_IBT))
Why static_cpu_has?
+ WARN_ONCE(1, "CET is disabled but got control protection fault\n");
"Control protection fault with CET support disabled\n"
quoted hunk ↗ jump to hunk
+ + tsk = current; + tsk->thread.error_code = error_code; + tsk->thread.trap_nr = X86_TRAP_CP; + + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && + printk_ratelimit()) { + unsigned int max_err; + unsigned long ssp; + + max_err = ARRAY_SIZE(control_protection_err) - 1; + if ((error_code < 0) || (error_code > max_err)) + error_code = 0;
<---- newline here.
quoted hunk ↗ jump to hunk
+ rdmsrl(MSR_IA32_PL3_SSP, ssp); + pr_info("%s[%d] control protection ip:%lx sp:%lx ssp:%lx error:%lx(%s)", + tsk->comm, task_pid_nr(tsk), + regs->ip, regs->sp, ssp, error_code, + control_protection_err[error_code]); + print_vma_addr(KERN_CONT " in ", regs->ip); + pr_cont("\n"); + }
...
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Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette