[PATCH v4 01/17] perf: Protect perf_guest_cbs with RCU
From: Sean Christopherson <seanjc@google.com>
Date: 2021-11-11 02:07:48
Also in:
kvm, kvmarm, linux-perf-users, linux-riscv, lkml, xen-devel
Subsystem:
arm pmu profiling and debugging, arm port, arm64 port (aarch64 architecture), c-sky architecture, performance events subsystem, risc-v architecture, the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Will Deacon, Mark Rutland, Russell King, Catalin Marinas, Guo Ren, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Paul Walmsley, Palmer Dabbelt, Albert Ou, Linus Torvalds, Thomas Gleixner, Borislav Petkov, Dave Hansen
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")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/arm/kernel/perf_callchain.c | 17 +++++++++++------
arch/arm64/kernel/perf_callchain.c | 18 ++++++++++++------
arch/csky/kernel/perf_callchain.c | 6 ++++--
arch/nds32/kernel/perf_event_cpu.c | 17 +++++++++++------
arch/riscv/kernel/perf_callchain.c | 7 +++++--
arch/x86/events/core.c | 17 +++++++++++------
arch/x86/events/intel/core.c | 9 ++++++---
include/linux/perf_event.h | 13 ++++++++++++-
kernel/events/core.c | 13 ++++++++++---
9 files changed, 82 insertions(+), 35 deletions(-)
diff --git a/arch/arm/kernel/perf_callchain.c b/arch/arm/kernel/perf_callchain.c
index 3b69a76d341e..1626dfc6f6ce 100644
--- a/arch/arm/kernel/perf_callchain.c
+++ b/arch/arm/kernel/perf_callchain.c@@ -62,9 +62,10 @@ user_backtrace(struct frame_tail __user *tail, void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct frame_tail __user *tail; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* We don't support guest os callchain now */ return; }
@@ -98,9 +99,10 @@ callchain_trace(struct stackframe *fr, void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct stackframe fr; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* We don't support guest os callchain now */ return; }
@@ -111,18 +113,21 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re unsigned long perf_instruction_pointer(struct pt_regs *regs) { - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) - return perf_guest_cbs->get_guest_ip(); + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); + + if (guest_cbs && guest_cbs->is_in_guest()) + return guest_cbs->get_guest_ip(); return instruction_pointer(regs); } unsigned long perf_misc_flags(struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); int misc = 0; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { - if (perf_guest_cbs->is_user_mode()) + if (guest_cbs && guest_cbs->is_in_guest()) { + if (guest_cbs->is_user_mode()) misc |= PERF_RECORD_MISC_GUEST_USER; else misc |= PERF_RECORD_MISC_GUEST_KERNEL;
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 4a72c2727309..86d9f2013172 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c@@ -102,7 +102,9 @@ compat_user_backtrace(struct compat_frame_tail __user *tail, void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); + + if (guest_cbs && guest_cbs->is_in_guest()) { /* We don't support guest os callchain now */ return; }
@@ -147,9 +149,10 @@ static bool callchain_trace(void *data, unsigned long pc) void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct stackframe frame; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* We don't support guest os callchain now */ return; }
@@ -160,18 +163,21 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, unsigned long perf_instruction_pointer(struct pt_regs *regs) { - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) - return perf_guest_cbs->get_guest_ip(); + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); + + if (guest_cbs && guest_cbs->is_in_guest()) + return guest_cbs->get_guest_ip(); return instruction_pointer(regs); } unsigned long perf_misc_flags(struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); int misc = 0; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { - if (perf_guest_cbs->is_user_mode()) + if (guest_cbs && guest_cbs->is_in_guest()) { + if (guest_cbs->is_user_mode()) misc |= PERF_RECORD_MISC_GUEST_USER; else misc |= PERF_RECORD_MISC_GUEST_KERNEL;
diff --git a/arch/csky/kernel/perf_callchain.c b/arch/csky/kernel/perf_callchain.c
index ab55e98ee8f6..35318a635a5f 100644
--- a/arch/csky/kernel/perf_callchain.c
+++ b/arch/csky/kernel/perf_callchain.c@@ -86,10 +86,11 @@ static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry, void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); unsigned long fp = 0; /* C-SKY does not support virtualization. */ - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) + if (guest_cbs && guest_cbs->is_in_guest()) return; fp = regs->regs[4];
@@ -110,10 +111,11 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry, void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct stackframe fr; /* C-SKY does not support virtualization. */ - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { pr_warn("C-SKY does not support perf in guest mode!"); return; }
diff --git a/arch/nds32/kernel/perf_event_cpu.c b/arch/nds32/kernel/perf_event_cpu.c
index 0ce6f9f307e6..f38791960781 100644
--- a/arch/nds32/kernel/perf_event_cpu.c
+++ b/arch/nds32/kernel/perf_event_cpu.c@@ -1363,6 +1363,7 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); unsigned long fp = 0; unsigned long gp = 0; unsigned long lp = 0;
@@ -1371,7 +1372,7 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, leaf_fp = 0; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* We don't support guest os callchain now */ return; }
@@ -1479,9 +1480,10 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct stackframe fr; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* We don't support guest os callchain now */ return; }
@@ -1493,20 +1495,23 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, unsigned long perf_instruction_pointer(struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); + /* However, NDS32 does not support virtualization */ - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) - return perf_guest_cbs->get_guest_ip(); + if (guest_cbs && guest_cbs->is_in_guest()) + return guest_cbs->get_guest_ip(); return instruction_pointer(regs); } unsigned long perf_misc_flags(struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); int misc = 0; /* However, NDS32 does not support virtualization */ - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { - if (perf_guest_cbs->is_user_mode()) + if (guest_cbs && guest_cbs->is_in_guest()) { + if (guest_cbs->is_user_mode()) misc |= PERF_RECORD_MISC_GUEST_USER; else misc |= PERF_RECORD_MISC_GUEST_KERNEL;
diff --git a/arch/riscv/kernel/perf_callchain.c b/arch/riscv/kernel/perf_callchain.c
index 0bb1854dce83..8ecfc4c128bc 100644
--- a/arch/riscv/kernel/perf_callchain.c
+++ b/arch/riscv/kernel/perf_callchain.c@@ -56,10 +56,11 @@ static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry, void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); unsigned long fp = 0; /* RISC-V does not support perf in guest mode. */ - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) + if (guest_cbs && guest_cbs->is_in_guest()) return; fp = regs->s0;
@@ -78,8 +79,10 @@ static bool fill_callchain(void *entry, unsigned long pc) void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); + /* RISC-V does not support perf in guest mode. */ - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { pr_warn("RISC-V does not support perf in guest mode!"); return; }
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 38b2c779146f..32cec290d3ad 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c@@ -2768,10 +2768,11 @@ static bool perf_hw_regs(struct pt_regs *regs) void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct unwind_state state; unsigned long addr; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* TODO: We don't support guest os callchain now */ return; }
@@ -2871,10 +2872,11 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); struct stack_frame frame; const struct stack_frame __user *fp; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { + if (guest_cbs && guest_cbs->is_in_guest()) { /* TODO: We don't support guest os callchain now */ return; }
@@ -2951,18 +2953,21 @@ static unsigned long code_segment_base(struct pt_regs *regs) unsigned long perf_instruction_pointer(struct pt_regs *regs) { - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) - return perf_guest_cbs->get_guest_ip(); + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); + + if (guest_cbs && guest_cbs->is_in_guest()) + return guest_cbs->get_guest_ip(); return regs->ip + code_segment_base(regs); } unsigned long perf_misc_flags(struct pt_regs *regs) { + struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); int misc = 0; - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { - if (perf_guest_cbs->is_user_mode()) + if (guest_cbs && guest_cbs->is_in_guest()) { + if (guest_cbs->is_user_mode()) misc |= PERF_RECORD_MISC_GUEST_USER; else misc |= PERF_RECORD_MISC_GUEST_KERNEL;
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 603964408d2d..cde29bd5bb53 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c@@ -2837,6 +2837,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) { struct perf_sample_data data; struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); + struct perf_guest_info_callbacks *guest_cbs; int bit; int handled = 0; u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
@@ -2903,9 +2904,11 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) */ if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) { handled++; - if (unlikely(perf_guest_cbs && perf_guest_cbs->is_in_guest() && - perf_guest_cbs->handle_intel_pt_intr)) - perf_guest_cbs->handle_intel_pt_intr(); + + guest_cbs = perf_get_guest_cbs(); + if (unlikely(guest_cbs && guest_cbs->is_in_guest() && + guest_cbs->handle_intel_pt_intr)) + guest_cbs->handle_intel_pt_intr(); else intel_pt_interrupt(); }
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0dcfd265beed..318c489b735b 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h@@ -1240,7 +1240,18 @@ extern void perf_event_bpf_event(struct bpf_prog *prog, enum perf_bpf_event_type type, u16 flags); -extern struct perf_guest_info_callbacks *perf_guest_cbs; +extern struct perf_guest_info_callbacks __rcu *perf_guest_cbs; +static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void) +{ + /* + * Callbacks are RCU-protected and must be READ_ONCE to avoid reloading + * the callbacks between a !NULL check and dereferences, to ensure + * pending stores/changes to the callback pointers are visible before a + * non-NULL perf_guest_cbs is visible to readers, and to prevent a + * module from unloading callbacks while readers are active. + */ + return rcu_dereference(perf_guest_cbs); +} extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks); extern int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f2253ea729a2..0cc775f702f8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c@@ -6526,18 +6526,25 @@ static void perf_pending_event(struct irq_work *entry) * Later on, we might change it to a list if there is * another virtualization implementation supporting the callbacks. */ -struct perf_guest_info_callbacks *perf_guest_cbs; +struct perf_guest_info_callbacks __rcu *perf_guest_cbs; int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) { - perf_guest_cbs = cbs; + if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs))) + return -EBUSY; + + rcu_assign_pointer(perf_guest_cbs, cbs); return 0; } EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) { - perf_guest_cbs = NULL; + if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs) != cbs)) + return -EINVAL; + + rcu_assign_pointer(perf_guest_cbs, NULL); + synchronize_rcu(); return 0; } EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
--
2.34.0.rc0.344.g81b53c2807-goog
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