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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>
This commit is contained in:
Max Filippov 2019-12-10 14:23:49 -08:00
parent 270a830691
commit a8f0c31fa8
4 changed files with 29 additions and 13 deletions
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11
arch/xtensa/Kconfig
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@ -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

24
arch/xtensa/kernel/traps.c
View File

@ -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_MULTIHIT, 0, do_multihit },
{ EXCCAUSE_ITLB_PRIVILEGE, 0, do_page_fault },
/* EXCCAUSE_SIZE_RESTRICTION unhandled */
{ 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_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_FETCH_CACHE_ATTRIBUTE, 0, do_page_fault },
{ EXCCAUSE_DTLB_MULTIHIT, 0, do_multihit },
{ 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),

3
arch/xtensa/mm/Makefile
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@ -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

4
arch/xtensa/mm/fault.c
View File

@ -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,