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linux_dsm_epyc7002/arch/powerpc/mm/fault.c
John Sperbeck ecb101aed8 powerpc/mm: Fix SEGV on mapped region to return SEGV_ACCERR 
The recent refactoring of the powerpc page fault handler in commit
c3350602e8 ("powerpc/mm: Make bad_area* helper functions") caused
access to protected memory regions to indicate SEGV_MAPERR instead of
the traditional SEGV_ACCERR in the si_code field of a user-space
signal handler. This can confuse debug libraries that temporarily
change the protection of memory regions, and expect to use SEGV_ACCERR
as an indication to restore access to a region.

This commit restores the previous behavior. The following program
exhibits the issue:

    $ ./repro read  || echo "FAILED"
    $ ./repro write || echo "FAILED"
    $ ./repro exec  || echo "FAILED"

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <signal.h>
    #include <sys/mman.h>
    #include <assert.h>

    static void segv_handler(int n, siginfo_t *info, void *arg) {
            _exit(info->si_code == SEGV_ACCERR ? 0 : 1);
    }

    int main(int argc, char **argv)
    {
            void *p = NULL;
            struct sigaction act = {
                    .sa_sigaction = segv_handler,
                    .sa_flags = SA_SIGINFO,
            };

            assert(argc == 2);
            p = mmap(NULL, getpagesize(),
                    (strcmp(argv[1], "write") == 0) ? PROT_READ : 0,
                    MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
            assert(p != MAP_FAILED);

            assert(sigaction(SIGSEGV, &act, NULL) == 0);
            if (strcmp(argv[1], "read") == 0)
                    printf("%c", *(unsigned char *)p);
            else if (strcmp(argv[1], "write") == 0)
                    *(unsigned char *)p = 0;
            else if (strcmp(argv[1], "exec") == 0)
                    ((void (*)(void))p)();
            return 1;  /* failed to generate SEGV */
    }

Fixes: c3350602e8 ("powerpc/mm: Make bad_area* helper functions")
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: John Sperbeck <jsperbeck@google.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[mpe: Add commit references in change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-01-02 21:12:33 +11:00

607 lines
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/*
* PowerPC version
* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
*
* Derived from "arch/i386/mm/fault.c"
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*
* Modified by Cort Dougan and Paul Mackerras.
*
* Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/highmem.h>
#include <linux/extable.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/perf_event.h>
#include <linux/ratelimit.h>
#include <linux/context_tracking.h>
#include <linux/hugetlb.h>
#include <linux/uaccess.h>
#include <asm/firmware.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include <asm/siginfo.h>
#include <asm/debug.h>
static inline bool notify_page_fault(struct pt_regs *regs)
{
bool ret = false;
#ifdef CONFIG_KPROBES
/* kprobe_running() needs smp_processor_id() */
if (!user_mode(regs)) {
preempt_disable();
if (kprobe_running() && kprobe_fault_handler(regs, 11))
ret = true;
preempt_enable();
}
#endif /* CONFIG_KPROBES */
if (unlikely(debugger_fault_handler(regs)))
ret = true;
return ret;
}
/*
* Check whether the instruction at regs->nip is a store using
* an update addressing form which will update r1.
*/
static bool store_updates_sp(struct pt_regs *regs)
{
unsigned int inst;
if (get_user(inst, (unsigned int __user *)regs->nip))
return false;
/* check for 1 in the rA field */
if (((inst >> 16) & 0x1f) != 1)
return false;
/* check major opcode */
switch (inst >> 26) {
case 37: /* stwu */
case 39: /* stbu */
case 45: /* sthu */
case 53: /* stfsu */
case 55: /* stfdu */
return true;
case 62: /* std or stdu */
return (inst & 3) == 1;
case 31:
/* check minor opcode */
switch ((inst >> 1) & 0x3ff) {
case 181: /* stdux */
case 183: /* stwux */
case 247: /* stbux */
case 439: /* sthux */
case 695: /* stfsux */
case 759: /* stfdux */
return true;
}
}
return false;
}
/*
* do_page_fault error handling helpers
*/
static int
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
{
/*
* If we are in kernel mode, bail out with a SEGV, this will
* be caught by the assembly which will restore the non-volatile
* registers before calling bad_page_fault()
*/
if (!user_mode(regs))
return SIGSEGV;
_exception(SIGSEGV, regs, si_code, address);
return 0;
}
static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
{
return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
}
static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
{
struct mm_struct *mm = current->mm;
/*
* Something tried to access memory that isn't in our memory map..
* Fix it, but check if it's kernel or user first..
*/
up_read(&mm->mmap_sem);
return __bad_area_nosemaphore(regs, address, si_code);
}
static noinline int bad_area(struct pt_regs *regs, unsigned long address)
{
return __bad_area(regs, address, SEGV_MAPERR);
}
static noinline int bad_access(struct pt_regs *regs, unsigned long address)
{
return __bad_area(regs, address, SEGV_ACCERR);
}
static int do_sigbus(struct pt_regs *regs, unsigned long address,
unsigned int fault)
{
siginfo_t info;
unsigned int lsb = 0;
if (!user_mode(regs))
return SIGBUS;
current->thread.trap_nr = BUS_ADRERR;
info.si_signo = SIGBUS;
info.si_errno = 0;
info.si_code = BUS_ADRERR;
info.si_addr = (void __user *)address;
#ifdef CONFIG_MEMORY_FAILURE
if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
current->comm, current->pid, address);
info.si_code = BUS_MCEERR_AR;
}
if (fault & VM_FAULT_HWPOISON_LARGE)
lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
if (fault & VM_FAULT_HWPOISON)
lsb = PAGE_SHIFT;
#endif
info.si_addr_lsb = lsb;
force_sig_info(SIGBUS, &info, current);
return 0;
}
static int mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
{
/*
* Kernel page fault interrupted by SIGKILL. We have no reason to
* continue processing.
*/
if (fatal_signal_pending(current) && !user_mode(regs))
return SIGKILL;
/* Out of memory */
if (fault & VM_FAULT_OOM) {
/*
* We ran out of memory, or some other thing happened to us that
* made us unable to handle the page fault gracefully.
*/
if (!user_mode(regs))
return SIGSEGV;
pagefault_out_of_memory();
} else {
if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
VM_FAULT_HWPOISON_LARGE))
return do_sigbus(regs, addr, fault);
else if (fault & VM_FAULT_SIGSEGV)
return bad_area_nosemaphore(regs, addr);
else
BUG();
}
return 0;
}
/* Is this a bad kernel fault ? */
static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
unsigned long address)
{
if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT))) {
printk_ratelimited(KERN_CRIT "kernel tried to execute"
" exec-protected page (%lx) -"
"exploit attempt? (uid: %d)\n",
address, from_kuid(&init_user_ns,
current_uid()));
}
return is_exec || (address >= TASK_SIZE);
}
static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
struct vm_area_struct *vma,
bool store_update_sp)
{
/*
* N.B. The POWER/Open ABI allows programs to access up to
* 288 bytes below the stack pointer.
* The kernel signal delivery code writes up to about 1.5kB
* below the stack pointer (r1) before decrementing it.
* The exec code can write slightly over 640kB to the stack
* before setting the user r1. Thus we allow the stack to
* expand to 1MB without further checks.
*/
if (address + 0x100000 < vma->vm_end) {
/* get user regs even if this fault is in kernel mode */
struct pt_regs *uregs = current->thread.regs;
if (uregs == NULL)
return true;
/*
* A user-mode access to an address a long way below
* the stack pointer is only valid if the instruction
* is one which would update the stack pointer to the
* address accessed if the instruction completed,
* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
* (or the byte, halfword, float or double forms).
*
* If we don't check this then any write to the area
* between the last mapped region and the stack will
* expand the stack rather than segfaulting.
*/
if (address + 2048 < uregs->gpr[1] && !store_update_sp)
return true;
}
return false;
}
static bool access_error(bool is_write, bool is_exec,
struct vm_area_struct *vma)
{
/*
* Allow execution from readable areas if the MMU does not
* provide separate controls over reading and executing.
*
* Note: That code used to not be enabled for 4xx/BookE.
* It is now as I/D cache coherency for these is done at
* set_pte_at() time and I see no reason why the test
* below wouldn't be valid on those processors. This -may-
* break programs compiled with a really old ABI though.
*/
if (is_exec) {
return !(vma->vm_flags & VM_EXEC) &&
(cpu_has_feature(CPU_FTR_NOEXECUTE) ||
!(vma->vm_flags & (VM_READ | VM_WRITE)));
}
if (is_write) {
if (unlikely(!(vma->vm_flags & VM_WRITE)))
return true;
return false;
}
if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
return true;
return false;
}
#ifdef CONFIG_PPC_SMLPAR
static inline void cmo_account_page_fault(void)
{
if (firmware_has_feature(FW_FEATURE_CMO)) {
u32 page_ins;
preempt_disable();
page_ins = be32_to_cpu(get_lppaca()->page_ins);
page_ins += 1 << PAGE_FACTOR;
get_lppaca()->page_ins = cpu_to_be32(page_ins);
preempt_enable();
}
}
#else
static inline void cmo_account_page_fault(void) { }
#endif /* CONFIG_PPC_SMLPAR */
#ifdef CONFIG_PPC_STD_MMU
static void sanity_check_fault(bool is_write, unsigned long error_code)
{
/*
* For hash translation mode, we should never get a
* PROTFAULT. Any update to pte to reduce access will result in us
* removing the hash page table entry, thus resulting in a DSISR_NOHPTE
* fault instead of DSISR_PROTFAULT.
*
* A pte update to relax the access will not result in a hash page table
* entry invalidate and hence can result in DSISR_PROTFAULT.
* ptep_set_access_flags() doesn't do a hpte flush. This is why we have
* the special !is_write in the below conditional.
*
* For platforms that doesn't supports coherent icache and do support
* per page noexec bit, we do setup things such that we do the
* sync between D/I cache via fault. But that is handled via low level
* hash fault code (hash_page_do_lazy_icache()) and we should not reach
* here in such case.
*
* For wrong access that can result in PROTFAULT, the above vma->vm_flags
* check should handle those and hence we should fall to the bad_area
* handling correctly.
*
* For embedded with per page exec support that doesn't support coherent
* icache we do get PROTFAULT and we handle that D/I cache sync in
* set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
* is conditional for server MMU.
*
* For radix, we can get prot fault for autonuma case, because radix
* page table will have them marked noaccess for user.
*/
if (!radix_enabled() && !is_write)
WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
}
#else
static void sanity_check_fault(bool is_write, unsigned long error_code) { }
#endif /* CONFIG_PPC_STD_MMU */
/*
* Define the correct "is_write" bit in error_code based
* on the processor family
*/
#if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
#define page_fault_is_write(__err) ((__err) & ESR_DST)
#define page_fault_is_bad(__err) (0)
#else
#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE)
#if defined(CONFIG_PPC_8xx)
#define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G)
#elif defined(CONFIG_PPC64)
#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_64S)
#else
#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S)
#endif
#endif
/*
* For 600- and 800-family processors, the error_code parameter is DSISR
* for a data fault, SRR1 for an instruction fault. For 400-family processors
* the error_code parameter is ESR for a data fault, 0 for an instruction
* fault.
* For 64-bit processors, the error_code parameter is
* - DSISR for a non-SLB data access fault,
* - SRR1 & 0x08000000 for a non-SLB instruction access fault
* - 0 any SLB fault.
*
* The return value is 0 if the fault was handled, or the signal
* number if this is a kernel fault that can't be handled here.
*/
static int __do_page_fault(struct pt_regs *regs, unsigned long address,
unsigned long error_code)
{
struct vm_area_struct * vma;
struct mm_struct *mm = current->mm;
unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
int is_exec = TRAP(regs) == 0x400;
int is_user = user_mode(regs);
int is_write = page_fault_is_write(error_code);
int fault, major = 0;
bool store_update_sp = false;
if (notify_page_fault(regs))
return 0;
if (unlikely(page_fault_is_bad(error_code))) {
if (is_user) {
_exception(SIGBUS, regs, BUS_OBJERR, address);
return 0;
}
return SIGBUS;
}
/* Additional sanity check(s) */
sanity_check_fault(is_write, error_code);
/*
* The kernel should never take an execute fault nor should it
* take a page fault to a kernel address.
*/
if (unlikely(!is_user && bad_kernel_fault(is_exec, error_code, address)))
return SIGSEGV;
/*
* If we're in an interrupt, have no user context or are running
* in a region with pagefaults disabled then we must not take the fault
*/
if (unlikely(faulthandler_disabled() || !mm)) {
if (is_user)
printk_ratelimited(KERN_ERR "Page fault in user mode"
" with faulthandler_disabled()=%d"
" mm=%p\n",
faulthandler_disabled(), mm);
return bad_area_nosemaphore(regs, address);
}
/* We restore the interrupt state now */
if (!arch_irq_disabled_regs(regs))
local_irq_enable();
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
/*
* We want to do this outside mmap_sem, because reading code around nip
* can result in fault, which will cause a deadlock when called with
* mmap_sem held
*/
if (is_write && is_user)
store_update_sp = store_updates_sp(regs);
if (is_user)
flags |= FAULT_FLAG_USER;
if (is_write)
flags |= FAULT_FLAG_WRITE;
if (is_exec)
flags |= FAULT_FLAG_INSTRUCTION;
/* When running in the kernel we expect faults to occur only to
* addresses in user space. All other faults represent errors in the
* kernel and should generate an OOPS. Unfortunately, in the case of an
* erroneous fault occurring in a code path which already holds mmap_sem
* we will deadlock attempting to validate the fault against the
* address space. Luckily the kernel only validly references user
* space from well defined areas of code, which are listed in the
* exceptions table.
*
* As the vast majority of faults will be valid we will only perform
* the source reference check when there is a possibility of a deadlock.
* Attempt to lock the address space, if we cannot we then validate the
* source. If this is invalid we can skip the address space check,
* thus avoiding the deadlock.
*/
if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
if (!is_user && !search_exception_tables(regs->nip))
return bad_area_nosemaphore(regs, address);
retry:
down_read(&mm->mmap_sem);
} else {
/*
* The above down_read_trylock() might have succeeded in
* which case we'll have missed the might_sleep() from
* down_read():
*/
might_sleep();
}
vma = find_vma(mm, address);
if (unlikely(!vma))
return bad_area(regs, address);
if (likely(vma->vm_start <= address))
goto good_area;
if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
return bad_area(regs, address);
/* The stack is being expanded, check if it's valid */
if (unlikely(bad_stack_expansion(regs, address, vma, store_update_sp)))
return bad_area(regs, address);
/* Try to expand it */
if (unlikely(expand_stack(vma, address)))
return bad_area(regs, address);
good_area:
if (unlikely(access_error(is_write, is_exec, vma)))
return bad_access(regs, address);
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
* the fault.
*/
fault = handle_mm_fault(vma, address, flags);
major |= fault & VM_FAULT_MAJOR;
/*
* Handle the retry right now, the mmap_sem has been released in that
* case.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
/* We retry only once */
if (flags & FAULT_FLAG_ALLOW_RETRY) {
/*
* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
* of starvation.
*/
flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
if (!fatal_signal_pending(current))
goto retry;
}
/*
* User mode? Just return to handle the fatal exception otherwise
* return to bad_page_fault
*/
return is_user ? 0 : SIGBUS;
}
up_read(&current->mm->mmap_sem);
if (unlikely(fault & VM_FAULT_ERROR))
return mm_fault_error(regs, address, fault);
/*
* Major/minor page fault accounting.
*/
if (major) {
current->maj_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
cmo_account_page_fault();
} else {
current->min_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
}
return 0;
}
NOKPROBE_SYMBOL(__do_page_fault);
int do_page_fault(struct pt_regs *regs, unsigned long address,
unsigned long error_code)
{
enum ctx_state prev_state = exception_enter();
int rc = __do_page_fault(regs, address, error_code);
exception_exit(prev_state);
return rc;
}
NOKPROBE_SYMBOL(do_page_fault);
/*
* bad_page_fault is called when we have a bad access from the kernel.
* It is called from the DSI and ISI handlers in head.S and from some
* of the procedures in traps.c.
*/
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
const struct exception_table_entry *entry;
/* Are we prepared to handle this fault? */
if ((entry = search_exception_tables(regs->nip)) != NULL) {
regs->nip = extable_fixup(entry);
return;
}
/* kernel has accessed a bad area */
switch (regs->trap) {
case 0x300:
case 0x380:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"data at address 0x%08lx\n", regs->dar);
break;
case 0x400:
case 0x480:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"instruction fetch\n");
break;
case 0x600:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"unaligned access at address 0x%08lx\n", regs->dar);
break;
default:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"unknown fault\n");
break;
}
printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
regs->nip);
if (task_stack_end_corrupted(current))
printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
die("Kernel access of bad area", regs, sig);
}
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