diff mbox series

[net-next,v5] net: skb: prevent the split of kfree_skb_reason() by gcc

Message ID 20220821051858.228284-1-imagedong@tencent.com (mailing list archive)
State Accepted
Commit c205cc7534a97f2d6fbd2a23a94ed7c036c6e2aa
Delegated to: Netdev Maintainers
Headers show
Series [net-next,v5] net: skb: prevent the split of kfree_skb_reason() by gcc | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Single patches do not need cover letters
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1811274 this patch: 1811274
netdev/cc_maintainers success CCed 8 of 8 maintainers
netdev/build_clang success Errors and warnings before: 4537 this patch: 4537
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1869290 this patch: 1869290
netdev/checkpatch fail ERROR: Macros with complex values should be enclosed in parentheses
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Menglong Dong Aug. 21, 2022, 5:18 a.m. UTC 
From: Menglong Dong <imagedong@tencent.com>

Sometimes, gcc will optimize the function by spliting it to two or
more functions. In this case, kfree_skb_reason() is splited to
kfree_skb_reason and kfree_skb_reason.part.0. However, the
function/tracepoint trace_kfree_skb() in it needs the return address
of kfree_skb_reason().

This split makes the call chains becomes:
  kfree_skb_reason() -> kfree_skb_reason.part.0 -> trace_kfree_skb()

which makes the return address that passed to trace_kfree_skb() be
kfree_skb().

Therefore, introduce '__fix_address', which is the combination of
'__noclone' and 'noinline', and apply it to kfree_skb_reason() to
prevent to from being splited or made inline.

(Is it better to simply apply '__noclone oninline' to kfree_skb_reason?
I'm thinking maybe other functions have the same problems)

Meanwhile, wrap 'skb_unref()' with 'unlikely()', as the compiler thinks
it is likely return true and splits kfree_skb_reason().

Signed-off-by: Menglong Dong <imagedong@tencent.com>
---
v5:
- replace optimize("O1") with '__noclone noinline', thanks for
  Segher Boessenkool and Nick Desaulniers's advice.
- wrap 'skb_unref()' with 'unlikely()', as Jakub Kicinski advise

v4:
- move the definition of __nofnsplit to compiler_attributes.h

v3:
- define __nofnsplit only for GCC
- add some document

v2:
- replace 'optimize' with '__optimize__' in __nofnsplit, as Miguel Ojeda
  advised.
---
 include/linux/compiler_attributes.h | 7 +++++++
 include/linux/skbuff.h              | 3 ++-
 net/core/skbuff.c                   | 5 +++--
 3 files changed, 12 insertions(+), 3 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Aug. 24, 2022, 9 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Sun, 21 Aug 2022 13:18:58 +0800 you wrote:
> From: Menglong Dong <imagedong@tencent.com>
> 
> Sometimes, gcc will optimize the function by spliting it to two or
> more functions. In this case, kfree_skb_reason() is splited to
> kfree_skb_reason and kfree_skb_reason.part.0. However, the
> function/tracepoint trace_kfree_skb() in it needs the return address
> of kfree_skb_reason().
> 
> [...]

Here is the summary with links:
  - [net-next,v5] net: skb: prevent the split of kfree_skb_reason() by gcc
    https://git.kernel.org/netdev/net-next/c/c205cc7534a9

You are awesome, thank you!
diff mbox series

Patch

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 445e80517cab..fc93c9488c76 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -371,4 +371,11 @@ 
  */
 #define __weak                          __attribute__((__weak__))
 
+/*
+ * Used by functions that use '__builtin_return_address'. These function
+ * don't want to be splited or made inline, which can make
+ * the '__builtin_return_address' get unexpected address.
+ */
+#define __fix_address noinline __noclone
+
 #endif /* __LINUX_COMPILER_ATTRIBUTES_H */
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 5d7ff8850eb2..4d0d3b4f0867 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1195,7 +1195,8 @@  static inline bool skb_unref(struct sk_buff *skb)
 	return true;
 }
 
-void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
+void __fix_address
+kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
 
 /**
  *	kfree_skb - free an sk_buff with 'NOT_SPECIFIED' reason
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 974bbbbe7138..35d9d5958dc6 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -777,9 +777,10 @@  EXPORT_SYMBOL(__kfree_skb);
  *	hit zero. Meanwhile, pass the drop reason to 'kfree_skb'
  *	tracepoint.
  */
-void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
+void __fix_address
+kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 {
-	if (!skb_unref(skb))
+	if (unlikely(!skb_unref(skb)))
 		return;
 
 	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);