Re: [PATCH RESEND 5/5] block: validate user space vectors during extraction

[Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Aug 05, 2026 / 21:46, Shin'ichiro Kawasaki wrote:
> Cc+: 0wnerD1ed
> 
> On Jul 20, 2026 / 13:10, Keith Busch wrote:
> > From: Keith Busch <kbusch@kernel.org>
> > 
> > The bio-based drivers don't necessarily check the alignment split, and
> > stacking block drivers don't always handle a misalignment detected after
> > submitting the bio. Validate user vectors against the device's
> > dma_alignment as the bio is built from the iov_iter, rejecting
> > misaligned early with -EINVAL.
> 
> Recently, the new test case block/045 was added to blkests through a GitHub PR
> [1]. The test case passes with the Linux master branch tags v7.2-rcX. Today, I
> found that it fails with block/for-next branch tip [2]. I bisected and found
> that this patch triggers the failure.
> 
> 0wnerDied, Keith, may I ask your help to resolve the failure? I'm guessing
> the test case needs to care device's dma alignment, but not so sure.

I took a closer look. I modified the test case to respect the dma alignment [*],
and now the test case passes. This approach looks working. Will post the change
as a formal patch for review.

[*] fix trial patch for blktests

diff --git a/src/bio-full-trim.c b/src/bio-full-trim.c
index e304b2c..7cea3f9 100644
--- a/src/bio-full-trim.c
+++ b/src/bio-full-trim.c
@@ -12,20 +12,38 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+int msb(unsigned int v)
+{
+	unsigned int b = 0;
+
+	while (v >>= 1)
+		b++;
+
+	return b;
+}
+
 int main(int argc, char **argv)
 {
 	unsigned int block_size;
 	unsigned char *p;
 	long page_size;
+	unsigned int dma_alignment;
+	unsigned int dma_aligned_offset;
 	ssize_t ret;
 	int fd;
 
-	if (argc != 2)
+	if (argc != 3)
 		return EXIT_FAILURE;
+
 	page_size = sysconf(_SC_PAGESIZE);
 	if (page_size <= 0)
 		errx(EXIT_FAILURE, "invalid page size");
 
+	dma_alignment = atoi(argv[2]);
+	dma_aligned_offset = 1 << (msb(dma_alignment) + 1);
+	if (dma_aligned_offset >= page_size)
+		err(EXIT_FAILURE, "unexpected dma_alignment");
+
 	fd = open(argv[1], O_RDONLY | O_DIRECT);
 	if (fd < 0)
 		err(EXIT_FAILURE, "open %s", argv[1]);
@@ -40,7 +58,7 @@ int main(int argc, char **argv)
 		err(EXIT_FAILURE, "mprotect");
 
 	errno = 0;
-	ret = pread(fd, p + page_size - 1, block_size, 0);
+	ret = pread(fd, p + page_size - dma_aligned_offset, block_size, 0);
 	if (ret == -1 && errno == EFAULT)
 		return EXIT_SUCCESS;
 	errx(EXIT_FAILURE, "pread returned %zd (errno %d)", ret, errno);
diff --git a/tests/block/045 b/tests/block/045
index 65bfcb9..6e112b6 100755
--- a/tests/block/045
+++ b/tests/block/045
@@ -25,7 +25,8 @@ test() {
 		return 1
 	fi
 
-	if ! src/bio-full-trim /dev/nullb1; then
+	if ! src/bio-full-trim /dev/nullb1 \
+	     $(< /sys/block/nullb1/queue/dma_alignment); then
 		echo "bio-full-trim helper failed"
 	fi
 
-- 
2.55.0