[PATCH 6.1.y] iommufd/iova_bitmap: Ensure that iova_bitmap_set() handles the full IOVA

[Sasha Levin <sashal@kernel.org>]

From: Andrea Parri <parri.andrea@gmail.com>

[ Upstream commit e21952d72b4740f08a272d694cca223b6b0099ca ]

Generally userspace is going to step the dirty bitmap through the IOVA
space. However if the bitmap ends in the middle of a large PTE this is
problematic. The first step will clear the dirty bit and report dirty to
the end of its bitmap while the second step will see the clear'd dirty and
report clean for the start of the bitmap. If it happens this ends up
losing dirties.

Further this function is missing bounds checking so if this does happen
ther is a good chance it will write memory beyond what the userspace was
expecting.

Return an error code if this illegal condition happens.

Fixes: 58ccf0190d19 ("vfio: Add an IOVA bitmap support")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Link: https://patch.msgid.link/20260925161142.189813-2-parri.andrea@gmail.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
[ sashal: adapted error propagation to the older VFIO window iterator using a newly added bitmap->err field ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/vfio/iova_bitmap.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/iova_bitmap.c b/drivers/vfio/iova_bitmap.c
index eab0de7799fa2..fc9d4ef74ddda 100644
--- a/drivers/vfio/iova_bitmap.c
+++ b/drivers/vfio/iova_bitmap.c
@@ -112,6 +112,8 @@ struct iova_bitmap {
 
 	/* length of the IOVA range for the whole bitmap */
 	size_t length;
+
+	int err;
 };
 
 /*
@@ -380,11 +382,11 @@ int iova_bitmap_for_each(struct iova_bitmap *bitmap, void *opaque,
 	     ret = iova_bitmap_advance(bitmap)) {
 		ret = fn(bitmap, iova_bitmap_mapped_iova(bitmap),
 			 iova_bitmap_mapped_length(bitmap), opaque);
-		if (ret)
+		if (ret || bitmap->err)
 			break;
 	}
 
-	return ret;
+	return ret ? ret : bitmap->err;
 }
 
 /**
@@ -407,6 +409,18 @@ void iova_bitmap_set(struct iova_bitmap *bitmap,
 			mapped->pgshift) + mapped->pgoff * BITS_PER_BYTE;
 	unsigned long last_page_idx = mapped->npages - 1;
 
+	/*
+	 * If the range cannot be recorded then the system call returns failure.
+	 * This is to prevent loosing dirties if userspace is expecting to step
+	 * the bitmap through the IOVA space.
+	 */
+	if (!length || length > bitmap->length || iova < bitmap->iova ||
+	    iova - bitmap->iova > bitmap->length - length) {
+		if (!bitmap->err)
+			bitmap->err = -EPROTO;
+		return;
+	}
+
 	do {
 		unsigned int page_idx = cur_bit / BITS_PER_PAGE;
 		unsigned int offset = cur_bit % BITS_PER_PAGE;
-- 
2.53.0