[PATCH v4 01/17] perf: Protect perf_guest_cbs with RCU
Sean Christopherson
seanjc at google.com
Wed Nov 10 18:07:22 PST 2021
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 at vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc at 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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