Resent due to some failure at my end. Apologies if it arrives twice.
>From 63e34d4106b4dd767f9bfce951f8a35f14b52072 Mon Sep 17 00:00:00 2001
From: Kevin Sheldrake <kevin.sheldrake@xxxxxxxxxxxxx>
Date: Thu, 5 Nov 2020 12:18:53 +0000
Subject: [PATCH] Update perf ring buffer to prevent corruption from
bpf_perf_output_event()
The bpf_perf_output_event() helper takes a sample size parameter of u64, but
the underlying perf ring buffer uses a u16 internally. This 64KB maximum size
has to also accommodate a variable sized header. Failure to observe this
restriction can result in corruption of the perf ring buffer as samples
overlap.
Track the sample size and return -E2BIG if too big to fit into the u16
size parameter.
Signed-off-by: Kevin Sheldrake <kevin.sheldrake@xxxxxxxxxxxxx>
---
include/linux/perf_event.h | 2 +-
kernel/events/core.c | 40 ++++++++++++++++++++++++++--------------
2 files changed, 27 insertions(+), 15 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0c19d27..b9802e5 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1060,7 +1060,7 @@ extern void perf_output_sample(struct perf_output_handle *handle,
struct perf_event_header *header,
struct perf_sample_data *data,
struct perf_event *event);
-extern void perf_prepare_sample(struct perf_event_header *header,
+extern int perf_prepare_sample(struct perf_event_header *header,
struct perf_sample_data *data,
struct perf_event *event,
struct pt_regs *regs);
diff --git a/kernel/events/core.c b/kernel/events/core.c
index da467e1..c6c4a3c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7016,15 +7016,17 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
return callchain ?: &__empty_callchain;
}
-void perf_prepare_sample(struct perf_event_header *header,
+int perf_prepare_sample(struct perf_event_header *header,
struct perf_sample_data *data,
struct perf_event *event,
struct pt_regs *regs)
{
u64 sample_type = event->attr.sample_type;
+ u32 header_size = header->size;
+
header->type = PERF_RECORD_SAMPLE;
- header->size = sizeof(*header) + event->header_size;
+ header_size = sizeof(*header) + event->header_size;
header->misc = 0;
header->misc |= perf_misc_flags(regs);
@@ -7042,7 +7044,7 @@ void perf_prepare_sample(struct perf_event_header *header,
size += data->callchain->nr;
- header->size += size * sizeof(u64);
+ header_size += size * sizeof(u64);
}
if (sample_type & PERF_SAMPLE_RAW) {
@@ -7067,7 +7069,7 @@ void perf_prepare_sample(struct perf_event_header *header,
size = sizeof(u64);
}
- header->size += size;
+ header_size += size;
}
if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
@@ -7079,7 +7081,7 @@ void perf_prepare_sample(struct perf_event_header *header,
size += data->br_stack->nr
* sizeof(struct perf_branch_entry);
}
- header->size += size;
+ header_size += size;
}
if (sample_type & (PERF_SAMPLE_REGS_USER | PERF_SAMPLE_STACK_USER))
@@ -7095,7 +7097,7 @@ void perf_prepare_sample(struct perf_event_header *header,
size += hweight64(mask) * sizeof(u64);
}
- header->size += size;
+ header_size += size;
}
if (sample_type & PERF_SAMPLE_STACK_USER) {
@@ -7108,7 +7110,7 @@ void perf_prepare_sample(struct perf_event_header *header,
u16 stack_size = event->attr.sample_stack_user;
u16 size = sizeof(u64);
- stack_size = perf_sample_ustack_size(stack_size, header->size,
+ stack_size = perf_sample_ustack_size(stack_size, header_size,
data->regs_user.regs);
/*
@@ -7120,7 +7122,7 @@ void perf_prepare_sample(struct perf_event_header *header,
size += sizeof(u64) + stack_size;
data->stack_user_size = stack_size;
- header->size += size;
+ header_size += size;
}
if (sample_type & PERF_SAMPLE_REGS_INTR) {
@@ -7135,7 +7137,7 @@ void perf_prepare_sample(struct perf_event_header *header,
size += hweight64(mask) * sizeof(u64);
}
- header->size += size;
+ header_size += size;
}
if (sample_type & PERF_SAMPLE_PHYS_ADDR)
@@ -7154,7 +7156,7 @@ void perf_prepare_sample(struct perf_event_header *header,
if (sample_type & PERF_SAMPLE_AUX) {
u64 size;
- header->size += sizeof(u64); /* size */
+ header_size += sizeof(u64); /* size */
/*
* Given the 16bit nature of header::size, an AUX sample can
@@ -7162,14 +7164,20 @@ void perf_prepare_sample(struct perf_event_header *header,
* Make sure this doesn't happen by using up to U16_MAX bytes
* per sample in total (rounded down to 8 byte boundary).
*/
- size = min_t(size_t, U16_MAX - header->size,
+ size = min_t(size_t, U16_MAX - header_size,
event->attr.aux_sample_size);
size = rounddown(size, 8);
size = perf_prepare_sample_aux(event, data, size);
- WARN_ON_ONCE(size + header->size > U16_MAX);
- header->size += size;
+ WARN_ON_ONCE(size + header_size > U16_MAX);
+ header_size += size;
}
+
+ if (header_size > U16_MAX)
+ return -E2BIG;
+
+ header->size = header_size;
+
/*
* If you're adding more sample types here, you likely need to do
* something about the overflowing header::size, like repurpose the
@@ -7179,6 +7187,8 @@ void perf_prepare_sample(struct perf_event_header *header,
* do here next.
*/
WARN_ON_ONCE(header->size & 7);
+
+ return 0;
}
static __always_inline int
@@ -7196,7 +7206,9 @@ __perf_event_output(struct perf_event *event,
/* protect the callchain buffers */
rcu_read_lock();
- perf_prepare_sample(&header, data, event, regs);
+ err = perf_prepare_sample(&header, data, event, regs);
+ if (err)
+ goto exit;
err = output_begin(&handle, event, header.size);
if (err)
--
2.7.4
