xtensa: noMMU: allow handling protection faults

Many xtensa CPU cores without full MMU still have memory protection
features capable of raising exceptions for invalid instruction
fetches/data access. Allow handling such exceptions. This improves
behavior of processes that pass invalid memory pointers to syscalls in
noMMU configs: in case of exception the kernel instead of killing the
process is now able to return -EINVAL from a syscall.

Introduce CONFIG_PFAULT that controls whether protection fault code is
enabled and register handlers for common memory protection exceptions
when it is enabled.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index bd113bc6e1925f6fdbe4e49c3350d24f3a4d6e99..bca2763495a1246073696c95a2ae9151a6e260b4 100644 (file)
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -79,6 +79,7 @@ config STACKTRACE_SUPPORT
 
 config MMU
        def_bool n
+       select PFAULT
 
 config HAVE_XTENSA_GPIO32
        def_bool n
@@ -178,6 +179,16 @@ config XTENSA_FAKE_NMI
 
          If unsure, say N.
 
+config PFAULT
+       bool "Handle protection faults" if EXPERT && !MMU
+       default y
+       help
+         Handle protection faults. MMU configurations must enable it.
+         noMMU configurations may disable it if used memory map never
+         generates protection faults or faults are always fatal.
+
+         If unsure, say Y.
+
 config XTENSA_UNALIGNED_USER
        bool "Unaligned memory access in user space"
        help

diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
index 9345007d474d311429e3b891ab2f1927dc2b03f9..82ced7b25b77cc23f11b7a468574bc81f64f8e79 100644 (file)
--- a/arch/xtensa/kernel/traps.c
+++ b/arch/xtensa/kernel/traps.c
@@ -110,21 +110,21 @@ static dispatch_init_table_t __initdata dispatch_init_table[] = {
 { EXCCAUSE_UNALIGNED,          KRNL,      fast_unaligned },
 #endif
 #ifdef CONFIG_MMU
-{ EXCCAUSE_ITLB_MISS,          0,         do_page_fault },
-{ EXCCAUSE_ITLB_MISS,          USER|KRNL, fast_second_level_miss},
+{ EXCCAUSE_ITLB_MISS,                  0,         do_page_fault },
+{ EXCCAUSE_ITLB_MISS,                  USER|KRNL, fast_second_level_miss},
+{ EXCCAUSE_DTLB_MISS,                  USER|KRNL, fast_second_level_miss},
+{ EXCCAUSE_DTLB_MISS,                  0,         do_page_fault },
+{ EXCCAUSE_STORE_CACHE_ATTRIBUTE,      USER|KRNL, fast_store_prohibited },
+#endif /* CONFIG_MMU */
+#ifdef CONFIG_PFAULT
 { EXCCAUSE_ITLB_MULTIHIT,              0,         do_multihit },
-{ EXCCAUSE_ITLB_PRIVILEGE,     0,         do_page_fault },
-/* EXCCAUSE_SIZE_RESTRICTION unhandled */
+{ EXCCAUSE_ITLB_PRIVILEGE,             0,         do_page_fault },
 { EXCCAUSE_FETCH_CACHE_ATTRIBUTE,      0,         do_page_fault },
-{ EXCCAUSE_DTLB_MISS,          USER|KRNL, fast_second_level_miss},
-{ EXCCAUSE_DTLB_MISS,          0,         do_page_fault },
 { EXCCAUSE_DTLB_MULTIHIT,              0,         do_multihit },
-{ EXCCAUSE_DTLB_PRIVILEGE,     0,         do_page_fault },
-/* EXCCAUSE_DTLB_SIZE_RESTRICTION unhandled */
-{ EXCCAUSE_STORE_CACHE_ATTRIBUTE,      USER|KRNL, fast_store_prohibited },
+{ EXCCAUSE_DTLB_PRIVILEGE,             0,         do_page_fault },
 { EXCCAUSE_STORE_CACHE_ATTRIBUTE,      0,         do_page_fault },
 { EXCCAUSE_LOAD_CACHE_ATTRIBUTE,       0,         do_page_fault },
-#endif /* CONFIG_MMU */
+#endif
 /* XCCHAL_EXCCAUSE_FLOATING_POINT unhandled */
 #if XTENSA_HAVE_COPROCESSOR(0)
 COPROCESSOR(0),

diff --git a/arch/xtensa/mm/Makefile b/arch/xtensa/mm/Makefile
index f7fb08ae768f2ebc1811f88d76cf2e920cb662f5..44153a335951afc7529190741b965476f744e4d7 100644 (file)
--- a/arch/xtensa/mm/Makefile
+++ b/arch/xtensa/mm/Makefile
@@ -4,7 +4,8 @@
 #
 
 obj-y                  := init.o misc.o
-obj-$(CONFIG_MMU)      += cache.o fault.o ioremap.o mmu.o tlb.o
+obj-$(CONFIG_PFAULT)   += fault.o
+obj-$(CONFIG_MMU)      += cache.o ioremap.o mmu.o tlb.o
 obj-$(CONFIG_HIGHMEM)  += highmem.o
 obj-$(CONFIG_KASAN)    += kasan_init.o
 

diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index 01e66da4a6b01a4d323890b9a6b8cd5c43a84a95..16f0a5ff57991c1135382594de7bb2ce5197cd70 100644 (file)
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -25,6 +25,7 @@ void bad_page_fault(struct pt_regs*, unsigned long, int);
 
 static void vmalloc_fault(struct pt_regs *regs, unsigned int address)
 {
+#ifdef CONFIG_MMU
        /* Synchronize this task's top level page-table
         * with the 'reference' page table.
         */
@@ -71,6 +72,9 @@ static void vmalloc_fault(struct pt_regs *regs, unsigned int address)
 
 bad_page_fault:
        bad_page_fault(regs, address, SIGKILL);
+#else
+       WARN_ONCE(1, "%s in noMMU configuration\n", __func__);
+#endif
 }
 /*
  * This routine handles page faults.  It determines the address,