linux-kernel - [PATCH] mm: fix KASAN build error due to p*d_populate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250821093542.37844-1-harry.yoo@oracle.com>
Date: Thu, 21 Aug 2025 18:35:42 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: harry.yoo@...cle.com
Cc: Liam.Howlett@...cle.com, akpm@...ux-foundation.org, andreyknvl@...il.com,
        aneesh.kumar@...ux.ibm.com, anshuman.khandual@....com,
        apopple@...dia.com, ardb@...nel.org, arnd@...db.de, bp@...en8.de,
        cl@...two.org, dave.hansen@...ux.intel.com, david@...hat.com,
        dennis@...nel.org, dev.jain@....com, dvyukov@...gle.com,
        glider@...gle.com, gwan-gyeong.mun@...el.com, hpa@...cr.com,
        jane.chu@...cle.com, jgross@...e.de, jhubbard@...dia.com,
        joao.m.martins@...cle.com, joro@...tes.org, kas@...nel.org,
        kevin.brodsky@....com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        lorenzo.stoakes@...cle.com, luto@...nel.org, maobibo@...ngson.cn,
        mhocko@...e.com, mingo@...hat.com, osalvador@...e.de,
        peterx@...hat.com, peterz@...radead.org, rppt@...nel.org,
        ryabinin.a.a@...il.com, ryan.roberts@....com, stable@...r.kernel.org,
        surenb@...gle.com, tglx@...utronix.de, thuth@...hat.com, tj@...nel.org,
        urezki@...il.com, vbabka@...e.cz, vincenzo.frascino@....com,
        x86@...nel.org, zhengqi.arch@...edance.com
Subject: [PATCH] mm: fix KASAN build error due to p*d_populate_kernel()

KASAN unconditionally references kasan_early_shadow_{p4d,pud}.
However, these global variables may not exist depending on the number of
page table levels. For example, if CONFIG_PGTABLE_LEVELS=3, both
variables do not exist. Although KASAN may refernce non-existent
variables, it didn't break builds because calls to {pgd,p4d}_populate()
are optimized away at compile time.

However, {pgd,p4d}_populate_kernel() is defined as a function regardless
of the number of page table levels, so the compiler may not optimize
them away. In this case, the following linker error occurs:

ld.lld: error: undefined symbol: kasan_early_shadow_p4d
>>> referenced by init.c:260 (/home/hyeyoo/mm-new/mm/kasan/init.c:260)
>>>               mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> referenced by init.c:260 (/home/hyeyoo/mm-new/mm/kasan/init.c:260)
>>>               mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> did you mean: kasan_early_shadow_pmd
>>> defined in: vmlinux.a(mm/kasan/init.o)

ld.lld: error: undefined symbol: kasan_early_shadow_pud
>>> referenced by init.c:263 (/home/hyeyoo/mm-new/mm/kasan/init.c:263)
>>>               mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> referenced by init.c:263 (/home/hyeyoo/mm-new/mm/kasan/init.c:263)
>>>               mm/kasan/init.o:(kasan_populate_early_shadow) in archive vmlinux.a
>>> referenced by init.c:200 (/home/hyeyoo/mm-new/mm/kasan/init.c:200)
>>>               mm/kasan/init.o:(zero_p4d_populate) in archive vmlinux.a
>>> referenced 1 more times

Therefore, to allow calls to {pgd,p4d}_populate_kernel() to be optimized
out at compile time, define {pgd,p4d}_populate_kernel() as macros.
This way, when pgd_populate() or p4d_populate() are simply empty macros,
the corresponding *_populate_kernel() functions can also be optimized
away.

Signed-off-by: Harry Yoo <harry.yoo@...cle.com>
---

While the description is quite verbose, it is intended to be fold-merged
into patch [1] of the page table sync series V5.

[1] https://lore.kernel.org/linux-mm/20250818020206.4517-3-harry.yoo@oracle.com/

 include/linux/pgalloc.h | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/include/linux/pgalloc.h b/include/linux/pgalloc.h
index 290ab864320f..8812f842978f 100644
--- a/include/linux/pgalloc.h
+++ b/include/linux/pgalloc.h
@@ -5,20 +5,18 @@
 #include <linux/pgtable.h>
 #include <asm/pgalloc.h>
 
-static inline void pgd_populate_kernel(unsigned long addr, pgd_t *pgd,
-				       p4d_t *p4d)
-{
-	pgd_populate(&init_mm, pgd, p4d);
-	if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED)
-		arch_sync_kernel_mappings(addr, addr);
-}
+#define pgd_populate_kernel(addr, pgd, p4d)				\
+	do {								\
+		pgd_populate(&init_mm, pgd, p4d);			\
+		if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED)	\
+			arch_sync_kernel_mappings(addr, addr);		\
+	} while (0)
 
-static inline void p4d_populate_kernel(unsigned long addr, p4d_t *p4d,
-				       pud_t *pud)
-{
-	p4d_populate(&init_mm, p4d, pud);
-	if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_P4D_MODIFIED)
-		arch_sync_kernel_mappings(addr, addr);
-}
+#define p4d_populate_kernel(addr, p4d, pud)				\
+	do {								\
+		p4d_populate(&init_mm, p4d, pud);			\
+		if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_P4D_MODIFIED)	\
+			arch_sync_kernel_mappings(addr, addr);		\
+	} while (0)
 
 #endif /* _LINUX_PGALLOC_H */
-- 
2.43.0