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From:   Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Kamal Dasu <kdasu.kdev@gmail.com>,
        Serge Semin <Sergey.Semin@baikalelectronics.ru>
Subject: [PATCH v2] MIPS: kernel: Reserve exception base early to prevent corruption
Date:   Sat,  6 Mar 2021 09:29:09 +0100
Message-Id: <20210306082910.3472-1-tsbogend@alpha.franken.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

BMIPS is one of the few platforms that do change the exception base.
After commit 2dcb39645441 ("memblock: do not start bottom-up allocations
with kernel_end") we started seeing BMIPS boards fail to boot with the
built-in FDT being corrupted.

Before the cited commit, early allocations would be in the [kernel_end,
RAM_END] range, but after commit they would be within [RAM_START +
PAGE_SIZE, RAM_END].

The custom exception base handler that is installed by
bmips_ebase_setup() done for BMIPS5000 CPUs ends-up trampling on the
memory region allocated by unflatten_and_copy_device_tree() thus
corrupting the FDT used by the kernel.

To fix this, we need to perform an early reservation of the custom
exception space. So we reserve it already in cpu_probe() for the CPUs
where this is fixed. For CPU with an ebase config register allocation
of exception space will be done in trap_init().

Huge thanks to Serget for analysing and proposing a solution to this
issue.

Fixes: 2dcb39645441 ("memblock: do not start bottom-up allocations with kernel_end")
Reported-by: Kamal Dasu <kdasu.kdev@gmail.com>
Debugged-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
Changes in v2:
 - do only memblock reservation in reserve_exception_space()
 - reserve 0..0x400 for all CPUs without ebase register and
   to addtional reserve_exception_space for BMIPS CPUs

 arch/mips/include/asm/traps.h    |  3 +++
 arch/mips/kernel/cpu-probe.c     |  7 +++++++
 arch/mips/kernel/cpu-r3k-probe.c |  3 +++
 arch/mips/kernel/traps.c         | 10 +++++-----
 4 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/mips/include/asm/traps.h b/arch/mips/include/asm/traps.h
index 6aa8f126a43d..b710e76c9c65 100644
--- a/arch/mips/include/asm/traps.h
+++ b/arch/mips/include/asm/traps.h
@@ -24,8 +24,11 @@ extern void (*board_ebase_setup)(void);
 extern void (*board_cache_error_setup)(void);
 
 extern int register_nmi_notifier(struct notifier_block *nb);
+extern void reserve_exception_space(phys_addr_t addr, unsigned long size);
 extern char except_vec_nmi[];
 
+#define VECTORSPACING 0x100	/* for EI/VI mode */
+
 #define nmi_notifier(fn, pri)						\
 ({									\
 	static struct notifier_block fn##_nb = {			\
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 9a89637b4ecf..b565bc4b900d 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -26,6 +26,7 @@
 #include <asm/elf.h>
 #include <asm/pgtable-bits.h>
 #include <asm/spram.h>
+#include <asm/traps.h>
 #include <linux/uaccess.h>
 
 #include "fpu-probe.h"
@@ -1628,6 +1629,7 @@ static inline void cpu_probe_broadcom(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_BMIPS3300;
 		__cpu_name[cpu] = "Broadcom BMIPS3300";
 		set_elf_platform(cpu, "bmips3300");
+		reserve_exception_space(0x400, VECTORSPACING * 64);
 		break;
 	case PRID_IMP_BMIPS43XX: {
 		int rev = c->processor_id & PRID_REV_MASK;
@@ -1638,6 +1640,7 @@ static inline void cpu_probe_broadcom(struct cpuinfo_mips *c, unsigned int cpu)
 			__cpu_name[cpu] = "Broadcom BMIPS4380";
 			set_elf_platform(cpu, "bmips4380");
 			c->options |= MIPS_CPU_RIXI;
+			reserve_exception_space(0x400, VECTORSPACING * 64);
 		} else {
 			c->cputype = CPU_BMIPS4350;
 			__cpu_name[cpu] = "Broadcom BMIPS4350";
@@ -1654,6 +1657,7 @@ static inline void cpu_probe_broadcom(struct cpuinfo_mips *c, unsigned int cpu)
 			__cpu_name[cpu] = "Broadcom BMIPS5000";
 		set_elf_platform(cpu, "bmips5000");
 		c->options |= MIPS_CPU_ULRI | MIPS_CPU_RIXI;
+		reserve_exception_space(0x1000, VECTORSPACING * 64);
 		break;
 	}
 }
@@ -2133,6 +2137,9 @@ void cpu_probe(void)
 	if (cpu == 0)
 		__ua_limit = ~((1ull << cpu_vmbits) - 1);
 #endif
+
+	if (cpu_has_mips_r2_r6)
+		reserve_exception_space(0, 0x400);
 }
 
 void cpu_report(void)
diff --git a/arch/mips/kernel/cpu-r3k-probe.c b/arch/mips/kernel/cpu-r3k-probe.c
index abdbbe8c5a43..af654771918c 100644
--- a/arch/mips/kernel/cpu-r3k-probe.c
+++ b/arch/mips/kernel/cpu-r3k-probe.c
@@ -21,6 +21,7 @@
 #include <asm/fpu.h>
 #include <asm/mipsregs.h>
 #include <asm/elf.h>
+#include <asm/traps.h>
 
 #include "fpu-probe.h"
 
@@ -158,6 +159,8 @@ void cpu_probe(void)
 		cpu_set_fpu_opts(c);
 	else
 		cpu_set_nofpu_opts(c);
+
+	reserve_exception_space(0, 0x400);
 }
 
 void cpu_report(void)
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index e0352958e2f7..808b8b61ded1 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -2009,13 +2009,16 @@ void __noreturn nmi_exception_handler(struct pt_regs *regs)
 	nmi_exit();
 }
 
-#define VECTORSPACING 0x100	/* for EI/VI mode */
-
 unsigned long ebase;
 EXPORT_SYMBOL_GPL(ebase);
 unsigned long exception_handlers[32];
 unsigned long vi_handlers[64];
 
+void reserve_exception_space(phys_addr_t addr, unsigned long size)
+{
+	memblock_reserve(addr, size);
+}
+
 void __init *set_except_vector(int n, void *addr)
 {
 	unsigned long handler = (unsigned long) addr;
@@ -2367,10 +2370,7 @@ void __init trap_init(void)
 
 	if (!cpu_has_mips_r2_r6) {
 		ebase = CAC_BASE;
-		ebase_pa = virt_to_phys((void *)ebase);
 		vec_size = 0x400;
-
-		memblock_reserve(ebase_pa, vec_size);
 	} else {
 		if (cpu_has_veic || cpu_has_vint)
 			vec_size = 0x200 + VECTORSPACING*64;
-- 
2.29.2