kernel/linux.git/arch/powerpc/mm/fault.c, branch linux-4.4.y

powerpc: Allow 4224 bytes of stack expansion for the signal frame

2020-08-26T08:27:09+00:00

commit 63dee5df43a31f3844efabc58972f0a206ca4534 upstream. We have powerpc specific logic in our page fault handling to decide if an access to an unmapped address below the stack pointer should expand the stack VMA. The code was originally added in 2004 "ported from 2.4". The rough logic is that the stack is allowed to grow to 1MB with no extra checking. Over 1MB the access must be within 2048 bytes of the stack pointer, or be from a user instruction that updates the stack pointer. The 2048 byte allowance below the stack pointer is there to cover the 288 byte "red zone" as well as the "about 1.5kB" needed by the signal delivery code. Unfortunately since then the signal frame has expanded, and is now 4224 bytes on 64-bit kernels with transactional memory enabled. This means if a process has consumed more than 1MB of stack, and its stack pointer lies less than 4224 bytes from the next page boundary, signal delivery will fault when trying to expand the stack and the process will see a SEGV. The total size of the signal frame is the size of struct rt_sigframe (which includes the red zone) plus __SIGNAL_FRAMESIZE (128 bytes on 64-bit). The 2048 byte allowance was correct until 2008 as the signal frame was: struct rt_sigframe { struct ucontext uc; /* 0 1440 */ /* --- cacheline 11 boundary (1408 bytes) was 32 bytes ago --- */ long unsigned int _unused[2]; /* 1440 16 */ unsigned int tramp[6]; /* 1456 24 */ struct siginfo * pinfo; /* 1480 8 */ void * puc; /* 1488 8 */ struct siginfo info; /* 1496 128 */ /* --- cacheline 12 boundary (1536 bytes) was 88 bytes ago --- */ char abigap[288]; /* 1624 288 */ /* size: 1920, cachelines: 15, members: 7 */ /* padding: 8 */ }; 1920 + 128 = 2048 Then in commit ce48b2100785 ("powerpc: Add VSX context save/restore, ptrace and signal support") (Jul 2008) the signal frame expanded to 2304 bytes: struct rt_sigframe { struct ucontext uc; /* 0 1696 */ <-- /* --- cacheline 13 boundary (1664 bytes) was 32 bytes ago --- */ long unsigned int _unused[2]; /* 1696 16 */ unsigned int tramp[6]; /* 1712 24 */ struct siginfo * pinfo; /* 1736 8 */ void * puc; /* 1744 8 */ struct siginfo info; /* 1752 128 */ /* --- cacheline 14 boundary (1792 bytes) was 88 bytes ago --- */ char abigap[288]; /* 1880 288 */ /* size: 2176, cachelines: 17, members: 7 */ /* padding: 8 */ }; 2176 + 128 = 2304 At this point we should have been exposed to the bug, though as far as I know it was never reported. I no longer have a system old enough to easily test on. Then in 2010 commit 320b2b8de126 ("mm: keep a guard page below a grow-down stack segment") caused our stack expansion code to never trigger, as there was always a VMA found for a write up to PAGE_SIZE below r1. That meant the bug was hidden as we continued to expand the signal frame in commit 2b0a576d15e0 ("powerpc: Add new transactional memory state to the signal context") (Feb 2013): struct rt_sigframe { struct ucontext uc; /* 0 1696 */ /* --- cacheline 13 boundary (1664 bytes) was 32 bytes ago --- */ struct ucontext uc_transact; /* 1696 1696 */ <-- /* --- cacheline 26 boundary (3328 bytes) was 64 bytes ago --- */ long unsigned int _unused[2]; /* 3392 16 */ unsigned int tramp[6]; /* 3408 24 */ struct siginfo * pinfo; /* 3432 8 */ void * puc; /* 3440 8 */ struct siginfo info; /* 3448 128 */ /* --- cacheline 27 boundary (3456 bytes) was 120 bytes ago --- */ char abigap[288]; /* 3576 288 */ /* size: 3872, cachelines: 31, members: 8 */ /* padding: 8 */ /* last cacheline: 32 bytes */ }; 3872 + 128 = 4000 And commit 573ebfa6601f ("powerpc: Increase stack redzone for 64-bit userspace to 512 bytes") (Feb 2014): struct rt_sigframe { struct ucontext uc; /* 0 1696 */ /* --- cacheline 13 boundary (1664 bytes) was 32 bytes ago --- */ struct ucontext uc_transact; /* 1696 1696 */ /* --- cacheline 26 boundary (3328 bytes) was 64 bytes ago --- */ long unsigned int _unused[2]; /* 3392 16 */ unsigned int tramp[6]; /* 3408 24 */ struct siginfo * pinfo; /* 3432 8 */ void * puc; /* 3440 8 */ struct siginfo info; /* 3448 128 */ /* --- cacheline 27 boundary (3456 bytes) was 120 bytes ago --- */ char abigap[512]; /* 3576 512 */ <-- /* size: 4096, cachelines: 32, members: 8 */ /* padding: 8 */ }; 4096 + 128 = 4224 Then finally in 2017, commit 1be7107fbe18 ("mm: larger stack guard gap, between vmas") exposed us to the existing bug, because it changed the stack VMA to be the correct/real size, meaning our stack expansion code is now triggered. Fix it by increasing the allowance to 4224 bytes. Hard-coding 4224 is obviously unsafe against future expansions of the signal frame in the same way as the existing code. We can't easily use sizeof() because the signal frame structure is not in a header. We will either fix that, or rip out all the custom stack expansion checking logic entirely. Fixes: ce48b2100785 ("powerpc: Add VSX context save/restore, ptrace and signal support") Cc: stable@vger.kernel.org # v2.6.27+ Reported-by: Tom Lane Tested-by: Daniel Axtens Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200724092528.1578671-2-mpe@ellerman.id.au Signed-off-by: Daniel Axtens Signed-off-by: Greg Kroah-Hartman

powerpc/mm: Make NULL pointer deferences explicit on bad page faults.

2019-12-05T14:26:58+00:00

[ Upstream commit 49a502ea23bf9dec47f8f3c3960909ff409cd1bb ] As several other arches including x86, this patch makes it explicit that a bad page fault is a NULL pointer dereference when the fault address is lower than PAGE_SIZE In the mean time, this page makes all bad_page_fault() messages shorter so that they remain on one single line. And it prefixes them by "BUG: " so that they get easily grepped. Signed-off-by: Christophe Leroy [mpe: Avoid pr_cont()] Signed-off-by: Michael Ellerman Signed-off-by: Sasha Levin

powerpc: Avoid taking a data miss on every userspace instruction miss

2018-03-22T08:23:23+00:00

[ Upstream commit a7a9dcd882a67b68568868b988289fce5ffd8419 ] Early on in do_page_fault() we call store_updates_sp(), regardless of the type of exception. For an instruction miss this doesn't make sense, because we only use this information to detect if a data miss is the result of a stack expansion instruction or not. Worse still, it results in a data miss within every userspace instruction miss handler, because we try and load the very instruction we are about to install a pte for! A simple exec microbenchmark runs 6% faster on POWER8 with this fix: #include #include #include int main(int argc, char *argv[]) { unsigned long left = atol(argv[1]); char leftstr[16]; if (left-- == 0) return 0; sprintf(leftstr, "%ld", left); execlp(argv[0], argv[0], leftstr, NULL); perror("exec failed\n"); return 0; } Pass the number of iterations on the command line (eg 10000) and time how long it takes to execute. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

powerpc: Add plain English description for alignment exception oopses

2015-07-06T10:24:35+00:00

If we take an alignment exception which we cannot fix, the oops currently prints: Unable to handle kernel paging request for unknown fault Lets print something more useful: Unable to handle kernel paging request for unaligned access at address 0xc0000000f77bba8f Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman

mm/fault, arch: Use pagefault_disable() to check for disabled pagefaults in the handler

2015-05-19T06:39:15+00:00

Introduce faulthandler_disabled() and use it to check for irq context and disabled pagefaults (via pagefault_disable()) in the pagefault handlers. Please note that we keep the in_atomic() checks in place - to detect whether in irq context (in which case preemption is always properly disabled). In contrast, preempt_disable() should never be used to disable pagefaults. With !CONFIG_PREEMPT_COUNT, preempt_disable() doesn't modify the preempt counter, and therefore the result of in_atomic() differs. We validate that condition by using might_fault() checks when calling might_sleep(). Therefore, add a comment to faulthandler_disabled(), describing why this is needed. faulthandler_disabled() and pagefault_disable() are defined in linux/uaccess.h, so let's properly add that include to all relevant files. This patch is based on a patch from Thomas Gleixner. Reviewed-and-tested-by: Thomas Gleixner Signed-off-by: David Hildenbrand Signed-off-by: Peter Zijlstra (Intel) Cc: David.Laight@ACULAB.COM Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: airlied@linux.ie Cc: akpm@linux-foundation.org Cc: benh@kernel.crashing.org Cc: bigeasy@linutronix.de Cc: borntraeger@de.ibm.com Cc: daniel.vetter@intel.com Cc: heiko.carstens@de.ibm.com Cc: herbert@gondor.apana.org.au Cc: hocko@suse.cz Cc: hughd@google.com Cc: mst@redhat.com Cc: paulus@samba.org Cc: ralf@linux-mips.org Cc: schwidefsky@de.ibm.com Cc: yang.shi@windriver.com Link: http://lkml.kernel.org/r/1431359540-32227-7-git-send-email-dahi@linux.vnet.ibm.com Signed-off-by: Ingo Molnar

ppc64: add paranoid warnings for unexpected DSISR_PROTFAULT

2015-02-13T02:54:08+00:00

ppc64 should not be depending on DSISR_PROTFAULT and it's unexpected if they are triggered. This patch adds warnings just in case they are being accidentally depended upon. Signed-off-by: Mel Gorman Acked-by: Aneesh Kumar K.V Tested-by: Sasha Levin Cc: Benjamin Herrenschmidt Cc: Dave Jones Cc: Hugh Dickins Cc: Ingo Molnar Cc: Kirill Shutemov Cc: Linus Torvalds Cc: Paul Mackerras Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: convert p[te|md]_numa users to p[te|md]_protnone_numa

2015-02-13T02:54:08+00:00

Convert existing users of pte_numa and friends to the new helper. Note that the kernel is broken after this patch is applied until the other page table modifiers are also altered. This patch layout is to make review easier. Signed-off-by: Mel Gorman Acked-by: Linus Torvalds Acked-by: Aneesh Kumar Acked-by: Benjamin Herrenschmidt Tested-by: Sasha Levin Cc: Dave Jones Cc: Hugh Dickins Cc: Ingo Molnar Cc: Kirill Shutemov Cc: Paul Mackerras Cc: Rik van Riel Cc: Sasha Levin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

vm: add VM_FAULT_SIGSEGV handling support

2015-01-29T18:51:32+00:00

The core VM already knows about VM_FAULT_SIGBUS, but cannot return a "you should SIGSEGV" error, because the SIGSEGV case was generally handled by the caller - usually the architecture fault handler. That results in lots of duplication - all the architecture fault handlers end up doing very similar "look up vma, check permissions, do retries etc" - but it generally works. However, there are cases where the VM actually wants to SIGSEGV, and applications _expect_ SIGSEGV. In particular, when accessing the stack guard page, libsigsegv expects a SIGSEGV. And it usually got one, because the stack growth is handled by that duplicated architecture fault handler. However, when the generic VM layer started propagating the error return from the stack expansion in commit fee7e49d4514 ("mm: propagate error from stack expansion even for guard page"), that now exposed the existing VM_FAULT_SIGBUS result to user space. And user space really expected SIGSEGV, not SIGBUS. To fix that case, we need to add a VM_FAULT_SIGSEGV, and teach all those duplicate architecture fault handlers about it. They all already have the code to handle SIGSEGV, so it's about just tying that new return value to the existing code, but it's all a bit annoying. This is the mindless minimal patch to do this. A more extensive patch would be to try to gather up the mostly shared fault handling logic into one generic helper routine, and long-term we really should do that cleanup. Just from this patch, you can generally see that most architectures just copied (directly or indirectly) the old x86 way of doing things, but in the meantime that original x86 model has been improved to hold the VM semaphore for shorter times etc and to handle VM_FAULT_RETRY and other "newer" things, so it would be a good idea to bring all those improvements to the generic case and teach other architectures about them too. Reported-and-tested-by: Takashi Iwai Tested-by: Jan Engelhardt Acked-by: Heiko Carstens # "s390 still compiles and boots" Cc: linux-arch@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds

powerpc/8xx: Invalidate non present TLB as early as possible

2014-11-08T00:10:45+00:00

8xx sometimes need to load a invalid/non-present TLBs in it DTLB asm handler. These must be invalidated separaly as linux mm doesn't. Commit 5efab4a02c89c252fb4cce097aafde5f8208dbfe was invalidating them in arch/powerpc/mm/fault.c. This patch does the invalidation earlier in order to free the TLB as soon as possible. This also has the advantage of removing some 8xx specific code from fault.c Signed-off-by: Christophe Leroy Signed-off-by: Scott Wood

Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2014-10-13T14:23:15+00:00

Pull scheduler updates from Ingo Molnar: "The main changes in this cycle were: - Optimized support for Intel "Cluster-on-Die" (CoD) topologies (Dave Hansen) - Various sched/idle refinements for better idle handling (Nicolas Pitre, Daniel Lezcano, Chuansheng Liu, Vincent Guittot) - sched/numa updates and optimizations (Rik van Riel) - sysbench speedup (Vincent Guittot) - capacity calculation cleanups/refactoring (Vincent Guittot) - Various cleanups to thread group iteration (Oleg Nesterov) - Double-rq-lock removal optimization and various refactorings (Kirill Tkhai) - various sched/deadline fixes ... and lots of other changes" * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (72 commits) sched/dl: Use dl_bw_of() under rcu_read_lock_sched() sched/fair: Delete resched_cpu() from idle_balance() sched, time: Fix build error with 64 bit cputime_t on 32 bit systems sched: Improve sysbench performance by fixing spurious active migration sched/x86: Fix up typo in topology detection x86, sched: Add new topology for multi-NUMA-node CPUs sched/rt: Use resched_curr() in task_tick_rt() sched: Use rq->rd in sched_setaffinity() under RCU read lock sched: cleanup: Rename 'out_unlock' to 'out_free_new_mask' sched: Use dl_bw_of() under RCU read lock sched/fair: Remove duplicate code from can_migrate_task() sched, mips, ia64: Remove __ARCH_WANT_UNLOCKED_CTXSW sched: print_rq(): Don't use tasklist_lock sched: normalize_rt_tasks(): Don't use _irqsave for tasklist_lock, use task_rq_lock() sched: Fix the task-group check in tg_has_rt_tasks() sched/fair: Leverage the idle state info when choosing the "idlest" cpu sched: Let the scheduler see CPU idle states sched/deadline: Fix inter- exclusive cpusets migrations sched/deadline: Clear dl_entity params when setscheduling to different class sched/numa: Kill the wrong/dead TASK_DEAD check in task_numa_fault() ...