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On some architectures, access_ok() does not do any argument type
checking, so replacing the definition with a generic one causes
a few warnings for harmless issues that were never caught before.
Fix the ones that I found either through my own test builds or
that were reported by the 0-day bot.
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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Drop "support" for guest callbacks from architectures that don't implement
the guest callbacks. Future patches will convert the callbacks to
static_call; rather than churn a bunch of arch code (that was presumably
copy+pasted from x86), remove it wholesale as it's useless and at best
wasting cycles.
A future patch will also add a Kconfig to force architcture to opt into
the callbacks to make it more difficult for uses "support" to sneak in in
the future.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-6-seanjc@google.com
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Protect perf_guest_cbs with RCU to fix multiple possible errors. Luckily,
all paths that read perf_guest_cbs already require RCU protection, e.g. to
protect the callback chains, so only the direct perf_guest_cbs touchpoints
need to be modified.
Bug #1 is a simple lack of WRITE_ONCE/READ_ONCE behavior to ensure
perf_guest_cbs isn't reloaded between a !NULL check and a dereference.
Fixed via the READ_ONCE() in rcu_dereference().
Bug #2 is that on weakly-ordered architectures, updates to the callbacks
themselves are not guaranteed to be visible before the pointer is made
visible to readers. Fixed by the smp_store_release() in
rcu_assign_pointer() when the new pointer is non-NULL.
Bug #3 is that, because the callbacks are global, it's possible for
readers to run in parallel with an unregisters, and thus a module
implementing the callbacks can be unloaded while readers are in flight,
resulting in a use-after-free. Fixed by a synchronize_rcu() call when
unregistering callbacks.
Bug #1 escaped notice because it's extremely unlikely a compiler will
reload perf_guest_cbs in this sequence. perf_guest_cbs does get reloaded
for future derefs, e.g. for ->is_user_mode(), but the ->is_in_guest()
guard all but guarantees the consumer will win the race, e.g. to nullify
perf_guest_cbs, KVM has to completely exit the guest and teardown down
all VMs before KVM start its module unload / unregister sequence. This
also makes it all but impossible to encounter bug #3.
Bug #2 has not been a problem because all architectures that register
callbacks are strongly ordered and/or have a static set of callbacks.
But with help, unloading kvm_intel can trigger bug #1 e.g. wrapping
perf_guest_cbs with READ_ONCE in perf_misc_flags() while spamming
kvm_intel module load/unload leads to:
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 6 PID: 1825 Comm: stress Not tainted 5.14.0-rc2+ #459
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:perf_misc_flags+0x1c/0x70
Call Trace:
perf_prepare_sample+0x53/0x6b0
perf_event_output_forward+0x67/0x160
__perf_event_overflow+0x52/0xf0
handle_pmi_common+0x207/0x300
intel_pmu_handle_irq+0xcf/0x410
perf_event_nmi_handler+0x28/0x50
nmi_handle+0xc7/0x260
default_do_nmi+0x6b/0x170
exc_nmi+0x103/0x130
asm_exc_nmi+0x76/0xbf
Fixes: 39447b386c84 ("perf: Enhance perf to allow for guest statistic collection from host")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211111020738.2512932-2-seanjc@google.com
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[ 5221.974084] Unable to handle kernel paging request at virtual address 0xfffff000, pc: 0x8002c18e
[ 5221.985929] Oops: 00000000
[ 5221.989488]
[ 5221.989488] CURRENT PROCESS:
[ 5221.989488]
[ 5221.992877] COMM=callchain_test PID=11962
[ 5221.995213] TEXT=00008000-000087e0 DATA=00009f1c-0000a018 BSS=0000a018-0000b000
[ 5221.999037] USER-STACK=7fc18e20 KERNEL-STACK=be204680
[ 5221.999037]
[ 5222.003292] PC: 0x8002c18e (perf_callchain_kernel+0x3e/0xd4)
[ 5222.007957] LR: 0x8002c198 (perf_callchain_kernel+0x48/0xd4)
[ 5222.074873] Call Trace:
[ 5222.074873] [<800a248e>] get_perf_callchain+0x20a/0x29c
[ 5222.074873] [<8009d964>] perf_callchain+0x64/0x80
[ 5222.074873] [<8009dc1c>] perf_prepare_sample+0x29c/0x4b8
[ 5222.074873] [<8009de6e>] perf_event_output_forward+0x36/0x98
[ 5222.074873] [<800497e0>] search_exception_tables+0x20/0x44
[ 5222.074873] [<8002cbb6>] do_page_fault+0x92/0x378
[ 5222.074873] [<80098608>] __perf_event_overflow+0x54/0xdc
[ 5222.074873] [<80098778>] perf_swevent_hrtimer+0xe8/0x164
[ 5222.074873] [<8002ddd0>] update_mmu_cache+0x0/0xd8
[ 5222.074873] [<8002c014>] user_backtrace+0x58/0xc4
[ 5222.074873] [<8002c0b4>] perf_callchain_user+0x34/0xd0
[ 5222.074873] [<800a2442>] get_perf_callchain+0x1be/0x29c
[ 5222.074873] [<8009d964>] perf_callchain+0x64/0x80
[ 5222.074873] [<8009d834>] perf_output_sample+0x78c/0x858
[ 5222.074873] [<8009dc1c>] perf_prepare_sample+0x29c/0x4b8
[ 5222.074873] [<8009de94>] perf_event_output_forward+0x5c/0x98
[ 5222.097846]
[ 5222.097846] [<800a0300>] perf_event_exit_task+0x58/0x43c
[ 5222.097846] [<8006c874>] hrtimer_interrupt+0x104/0x2ec
[ 5222.097846] [<800a0300>] perf_event_exit_task+0x58/0x43c
[ 5222.097846] [<80437bb6>] dw_apb_clockevent_irq+0x2a/0x4c
[ 5222.097846] [<8006c770>] hrtimer_interrupt+0x0/0x2ec
[ 5222.097846] [<8005f2e4>] __handle_irq_event_percpu+0xac/0x19c
[ 5222.097846] [<80437bb6>] dw_apb_clockevent_irq+0x2a/0x4c
[ 5222.097846] [<8005f408>] handle_irq_event_percpu+0x34/0x88
[ 5222.097846] [<8005f480>] handle_irq_event+0x24/0x64
[ 5222.097846] [<8006218c>] handle_level_irq+0x68/0xdc
[ 5222.097846] [<8005ec76>] __handle_domain_irq+0x56/0xa8
[ 5222.097846] [<80450e90>] ck_irq_handler+0xac/0xe4
[ 5222.097846] [<80029012>] csky_do_IRQ+0x12/0x24
[ 5222.097846] [<8002a3a0>] csky_irq+0x70/0x80
[ 5222.097846] [<800ca612>] alloc_set_pte+0xd2/0x238
[ 5222.097846] [<8002ddd0>] update_mmu_cache+0x0/0xd8
[ 5222.097846] [<800a0340>] perf_event_exit_task+0x98/0x43c
The original fp check doesn't base on the real kernal stack region.
Invalid fp address may cause kernel panic.
Signed-off-by: Mao Han <han_mao@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
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This patch add support for perf callchain sampling on csky platform.
As fp is used to unwind the stack, the program being sampled and the
C library need to be compiled with -mbacktrace for user callchains,
kernel callchains require CONFIG_STACKTRACE = y.
Changelog:
- Coding convention with Christoph's advice for riscv's.
Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Christoph Hellwig <hch@infradead.org>
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