From: Jocelyn Falempe <jfalempe@redhat.com>
Date: Thu, 9 Oct 2025 12:24:53 +0000 (+0200)
Subject: drm/panic: Fix 24bit pixel crossing page boundaries
X-Git-Tag: v6.17.6~44
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=91296c47dd76e82c15afb34def9d2ddd17df36a4;p=thirdparty%2Fkernel%2Fstable.git

drm/panic: Fix 24bit pixel crossing page boundaries

[ Upstream commit 23437509a69476d4f896891032d62ac868731668 ]

When using page list framebuffer, and using RGB888 format, some
pixels can cross the page boundaries, and this case was not handled,
leading to writing 1 or 2 bytes on the next virtual address.

Add a check and a specific function to handle this case.

Fixes: c9ff2808790f0 ("drm/panic: Add support to scanout buffer as array of pages")
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20251009122955.562888-7-jfalempe@redhat.com
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
index 1bc15c44207b..f52752880e1c 100644
--- a/drivers/gpu/drm/drm_panic.c
+++ b/drivers/gpu/drm/drm_panic.c
@@ -174,6 +174,33 @@ static void drm_panic_write_pixel24(void *vaddr, unsigned int offset, u32 color)
 	*p = color & 0xff;
 }
 
+/*
+ * Special case if the pixel crosses page boundaries
+ */
+static void drm_panic_write_pixel24_xpage(void *vaddr, struct page *next_page,
+					  unsigned int offset, u32 color)
+{
+	u8 *vaddr2;
+	u8 *p = vaddr + offset;
+
+	vaddr2 = kmap_local_page_try_from_panic(next_page);
+
+	*p++ = color & 0xff;
+	color >>= 8;
+
+	if (offset == PAGE_SIZE - 1)
+		p = vaddr2;
+
+	*p++ = color & 0xff;
+	color >>= 8;
+
+	if (offset == PAGE_SIZE - 2)
+		p = vaddr2;
+
+	*p = color & 0xff;
+	kunmap_local(vaddr2);
+}
+
 static void drm_panic_write_pixel32(void *vaddr, unsigned int offset, u32 color)
 {
 	u32 *p = vaddr + offset;
@@ -231,7 +258,14 @@ static void drm_panic_blit_page(struct page **pages, unsigned int dpitch,
 					page = new_page;
 					vaddr = kmap_local_page_try_from_panic(pages[page]);
 				}
-				if (vaddr)
+				if (!vaddr)
+					continue;
+
+				// Special case for 24bit, as a pixel might cross page boundaries
+				if (cpp == 3 && offset + 3 > PAGE_SIZE)
+					drm_panic_write_pixel24_xpage(vaddr, pages[page + 1],
+								      offset, fg32);
+				else
 					drm_panic_write_pixel(vaddr, offset, fg32, cpp);
 			}
 		}
@@ -321,7 +355,15 @@ static void drm_panic_fill_page(struct page **pages, unsigned int dpitch,
 				page = new_page;
 				vaddr = kmap_local_page_try_from_panic(pages[page]);
 			}
-			drm_panic_write_pixel(vaddr, offset, color, cpp);
+			if (!vaddr)
+				continue;
+
+			// Special case for 24bit, as a pixel might cross page boundaries
+			if (cpp == 3 && offset + 3 > PAGE_SIZE)
+				drm_panic_write_pixel24_xpage(vaddr, pages[page + 1],
+							      offset, color);
+			else
+				drm_panic_write_pixel(vaddr, offset, color, cpp);
 		}
 	}
 	if (vaddr)