Re: [PATCH v2 07/39] x86/cet: Add user control-protection fault handler
From: Andrew Cooper <hidden>
Date: 2022-10-05 01:21:10
Also in:
linux-arch, linux-doc, linux-mm, lkml
On 29/09/2022 23:29, Rick Edgecombe wrote:
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d62b2cb85cea..b7dde8730236 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c@@ -229,16 +223,74 @@ enum cp_error_code { CP_ENCL = 1 << 15, }; -DEFINE_IDTENTRY_ERRORCODE(exc_control_protection) +#ifdef CONFIG_X86_SHADOW_STACK +static const char * const control_protection_err[] = { + "unknown", + "near-ret", + "far-ret/iret", + "endbranch", + "rstorssp", + "setssbsy", +};
These are a mix of SHSTK and IBT errors. They should be inside
CONFIG_X86_CET using Kees' suggestion.
Also, if you express this as
static const char errors[][10] = {
[0] = "unknown",
[1] = "near ret",
[2] = "far/iret",
[3] = "endbranch",
[4] = "rstorssp",
[5] = "setssbsy",
};
then you can encode all the strings in roughly the space it takes to lay
out the pointers above.
+
+static DEFINE_RATELIMIT_STATE(cpf_rate, DEFAULT_RATELIMIT_INTERVAL,
+ DEFAULT_RATELIMIT_BURST);
+
+static void do_user_control_protection_fault(struct pt_regs *regs,
+ unsigned long error_code)
{
- if (!cpu_feature_enabled(X86_FEATURE_IBT)) {
- pr_err("Unexpected #CP\n");
- BUG();
+ struct task_struct *tsk;
+ unsigned long ssp;
+
+ /* Read SSP before enabling interrupts. */
+ rdmsrl(MSR_IA32_PL3_SSP, ssp);
+
+ cond_local_irq_enable(regs);
+
+ if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+ WARN_ONCE(1, "User-mode control protection fault with shadow support disabled\n");So it's ok to get an unexpected #CP on CET-capable hardware, but not on CET-incapable hardware? The conditions for this WARN() (and others) probably want adjusting to what the kernel has enabled, not what hardware is capable of.
quoted hunk ↗ jump to hunk
@@ -283,9 +335,29 @@ static int __init ibt_setup(char *str) } __setup("ibt=", ibt_setup); - +#else +static void do_kernel_control_protection_fault(struct pt_regs *regs) +{ + WARN_ONCE(1, "Kernel-mode control protection fault with IBT disabled\n"); +} #endif /* CONFIG_X86_KERNEL_IBT */ +#if defined(CONFIG_X86_KERNEL_IBT) || defined(CONFIG_X86_SHADOW_STACK) +DEFINE_IDTENTRY_ERRORCODE(exc_control_protection) +{ + if (!cpu_feature_enabled(X86_FEATURE_IBT) && + !cpu_feature_enabled(X86_FEATURE_SHSTK)) { + pr_err("Unexpected #CP\n");
Do some future poor sole a favour and render the numeric error code too. Without it, the error is ambiguous between SHSTK and IBT when %rip points at a call/ret instruction. ~Andrew