linux-kernel - [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP

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Date:   Wed, 12 Jul 2017 23:33:03 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     ard.biesheuvel@...aro.org, kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     akashi.takahiro@...aro.org, catalin.marinas@....com,
        dave.martin@....com, james.morse@....com,
        labbott@...oraproject.org, will.deacon@....com,
        keescook@...omium.org, Mark Rutland <mark.rutland@....com>
Subject: [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP

Signed-off-by: Mark Rutland <mark.rutland@....com>
---
 arch/arm64/Kconfig        |  1 +
 arch/arm64/kernel/entry.S | 43 +++++++++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/traps.c | 21 +++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b2024db..5cbd961 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1,5 +1,6 @@
 config ARM64
 	def_bool y
+	select HAVE_ARCH_VMAP_STACK
 	select ACPI_CCA_REQUIRED if ACPI
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_GTDT if ACPI
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 7c8b164..e0fdb65 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -396,11 +396,54 @@ el1_error_invalid:
 	inv_entry 1, BAD_ERROR
 ENDPROC(el1_error_invalid)
 
+#ifdef CONFIG_VMAP_STACK
+.macro detect_bad_stack
+	msr	sp_el0, x0
+	get_thread_info	x0
+	ldr	x0, [x0, #TSK_TI_CUR_STK]
+	sub	x0, sp, x0
+	and	x0, x0, #~(THREAD_SIZE - 1)
+	cbnz	x0, __bad_stack
+	mrs	x0, sp_el0
+.endm
+
+__bad_stack:
+	/*
+	 * Stash the bad SP, and free up another GPR. We no longer care about
+	 * EL0 state, since this thread cannot recover.
+	 */
+	mov	x0, sp
+	msr	tpidrro_el0, x0
+	msr	tpidr_el0, x1
+
+	/* Move to the emergency stack */
+	adr_this_cpu	x0, bad_stack, x1
+	mov	x1, #THREAD_START_SP
+	add	sp, x0, x1
+
+	/* Restore GPRs and log them to pt_regs */
+	mrs	x0, sp_el0
+	mrs	x1, tpidr_el0
+	kernel_entry 1
+
+	/* restore the bad SP to pt_regs */
+	mrs	x1, tpidrro_el0
+	str	x1, [sp, #S_SP]
+
+	/* Time to die */
+	mov	x0, sp
+	b	handle_bad_stack
+#else
+.macro detect_bad_stack
+.endm
+#endif
+
 /*
  * EL1 mode handlers.
  */
 	.align	6
 el1_sync:
+	detect_bad_stack
 	kernel_entry 1
 	mrs	x1, esr_el1			// read the syndrome register
 	lsr	x24, x1, #ESR_ELx_EC_SHIFT	// exception class
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 0805b44..84b00e3 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -683,6 +683,27 @@ asmlinkage void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr)
 	force_sig_info(info.si_signo, &info, current);
 }
 
+#ifdef CONFIG_VMAP_STACK
+DEFINE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], bad_stack) __aligned(16);
+
+asmlinkage void handle_bad_stack(struct pt_regs *regs)
+{
+	unsigned long tsk_stk = (unsigned long)current->stack;
+	unsigned long irq_stk = (unsigned long)per_cpu(irq_stack, smp_processor_id());
+
+	console_verbose();
+	pr_emerg("Stack out-of-bounds!\n"
+		 "\tsp: 0x%016lx\n"
+		 "\ttsk stack: [0x%016lx..0x%016lx]\n"
+		 "\tirq stack: [0x%016lx..0x%016lx]\n",
+		 kernel_stack_pointer(regs),
+		 tsk_stk, tsk_stk + THREAD_SIZE,
+		 irq_stk, irq_stk + THREAD_SIZE);
+	show_regs(regs);
+	panic("stack out-of-bounds");
+}
+#endif
+
 void __pte_error(const char *file, int line, unsigned long val)
 {
 	pr_err("%s:%d: bad pte %016lx.\n", file, line, val);
-- 
1.9.1