linux-kernel - [PATCH v3 1/1] pgo: Fix allocate

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Message-Id: <20210604165819.7947-1-jarmo.tiitto@gmail.com>
Date:   Fri,  4 Jun 2021 19:58:20 +0300
From:   Jarmo Tiitto <jarmo.tiitto@...il.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>,
        Bill Wendling <wcw@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Cc:     Jarmo Tiitto <jarmo.tiitto@...il.com>, morbo@...gle.com
Subject: [PATCH v3 1/1] pgo: Fix allocate_node() v2

When clang instrumentation eventually calls allocate_node()
the struct llvm_prf_data *p argument tells us from what section
we should reserve the vnode: It either points into vmlinux's
core __llvm_prf_data section or some loaded module's
__llvm_prf_data section.

But since we don't have access to corresponding
__llvm_prf_vnds section(s) for any module, the function
should return just NULL and ignore any profiling attempts
from modules for now.

Signed-off-by: Jarmo Tiitto <jarmo.tiitto@...il.com>
---
Based on Kees and others feedback here is v3 patch
that clarifies why the current checks in allocate_node()
are flawed. I did fair amount of KGDB time on it.

The commit is based on kees/for-next/clang/features tree,
hopefully this is ok. Should I have based it on linux-next
instead?

I grep -R'd where the memory_contains() can be found and it is only
found in #include <asm-generic/sections.h>

I cross my fingers and await if this is my first accepted patch. :-)
---
 kernel/pgo/instrument.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
index 0e07ee1b17d9..c69b4f7ebaad 100644
--- a/kernel/pgo/instrument.c
+++ b/kernel/pgo/instrument.c
@@ -18,6 +18,7 @@
 
 #define pr_fmt(fmt)	"pgo: " fmt
 
+#include <asm-generic/sections.h>
 #include <linux/bitops.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
@@ -55,17 +56,21 @@ void prf_unlock(unsigned long flags)
 static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
 						 u32 index, u64 value)
 {
-	if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
-		return NULL; /* Out of nodes */
-
-	current_node++;
-
-	/* Make sure the node is entirely within the section */
-	if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
-	    &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
+	const int max_vnds = prf_vnds_count();
+
+	/*
+	 * Check that p is within vmlinux __llvm_prf_data section.
+	 * If not, don't allocate since we can't handle modules yet.
+	 */
+	if (!memory_contains(__llvm_prf_data_start,
+		__llvm_prf_data_end, p, sizeof(*p)))
 		return NULL;
 
-	return &__llvm_prf_vnds_start[current_node];
+	if (WARN_ON_ONCE(current_node >= max_vnds))
+		return NULL; /* Out of nodes */
+
+	/* reserve vnode for vmlinux */
+	return &__llvm_prf_vnds_start[current_node++];
 }
 
 /*

base-commit: 5d0cda65918279ada060417c5fecb7e86ccb3def
-- 
2.31.1