On Wed, Feb 03, 2021 at 12:03:07PM -0800, Kees Cook wrote:

On Wed, Feb 03, 2021 at 11:48:40AM -0700, Nathan Chancellor wrote:

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On Tue, Jan 12, 2021 at 12:16:34PM -0700, Nathan Chancellor wrote:

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On Wed, Dec 30, 2020 at 04:40:40PM +0100, Arnd Bergmann wrote:

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From: Arnd Bergmann <arnd@arndb.de>

clang cannt evaluate this function argument at compile time
when the function is not inlined, which leads to a link
time failure:

ld.lld: error: undefined symbol: __compiletime_assert_414

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referenced by mremap.c
              mremap.o:(get_extent) in archive mm/built-in.a

Mark the function as __always_inline to avoid it.

Fixes: 9ad9718bfa41 ("mm/mremap: calculate extent in one place")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

I would like to see some movement on getting this fixed in 5.11. As it
stands, this is one of three __compiletime_assert references with
CONFIG_UBSAN_UNSIGNED_OVERFLOW. If we want to keep the BUILD_BUG()
around, I think this is fine. Alternatively, turning it into a runtime
check would be fine too.

Reviewed-by: Nathan Chancellor <redacted>

Ping? It is pretty late into the 5.11 cycle and this is still broken.

I think we should just do the __always_inline. Who can take this?

This should probably go through -mm, unless we get an ack then Nick and
I could take it.

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Cheers,
Nathan

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---
 mm/mremap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index c5590afe7165..1cb464a07184 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c

@@ -336,8 +336,9 @@ enum pgt_entry {
  * valid. Else returns a smaller extent bounded by the end of the source and
  * destination pgt_entry.
  */
-static unsigned long get_extent(enum pgt_entry entry, unsigned long old_addr,
-			unsigned long old_end, unsigned long new_addr)
+static __always_inline unsigned long get_extent(enum pgt_entry entry,
+			unsigned long old_addr, unsigned long old_end,
+			unsigned long new_addr)
 {
 	unsigned long next, extent, mask, size;
 

-- 
2.29.2

Cheers,
Nathan