From e0a890ceb0af55258db6d48b5af297bca794f0fa Mon Sep 17 00:00:00 2001 From: Alyssa Rosenzweig Date: Tue, 24 Aug 2021 13:30:25 -0400 Subject: [PATCH] drm/panfrost: Simplify lock_region calculation commit b5fab345654c603c07525100d744498f28786929 upstream. In lock_region, simplify the calculation of the region_width parameter. This field is the size, but encoded as ceil(log2(size)) - 1. ceil(log2(size)) may be computed directly as fls(size - 1). However, we want to use the 64-bit versions as the amount to lock can exceed 32-bits. This avoids undefined (and completely wrong) behaviour when locking all memory (size ~0). In this case, the old code would "round up" ~0 to the nearest page, overflowing to 0. Since fls(0) == 0, this would calculate a region width of 10 + 0 = 10. But then the code would shift by (region_width - 11) = -1. As shifting by a negative number is undefined, UBSAN flags the bug. Of course, even if it were defined the behaviour is wrong, instead of locking all memory almost none would get locked. The new form of the calculation corrects this special case and avoids the undefined behaviour. Signed-off-by: Alyssa Rosenzweig Reported-and-tested-by: Chris Morgan Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver") Cc: Reviewed-by: Steven Price Reviewed-by: Rob Herring Signed-off-by: Steven Price Link: https://patchwork.freedesktop.org/patch/msgid/20210824173028.7528-2-alyssa.rosenzweig@collabora.com Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/panfrost/panfrost_mmu.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-) diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c index 569509c2ba27a..397615638ecda 100644 --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c @@ -59,21 +59,12 @@ static void lock_region(struct panfrost_device *pfdev, u32 as_nr, { u8 region_width; u64 region = iova & PAGE_MASK; - /* - * fls returns: - * 1 .. 32 - * - * 10 + fls(num_pages) - * results in the range (11 .. 42) - */ - - size = round_up(size, PAGE_SIZE); - region_width = 10 + fls(size >> PAGE_SHIFT); - if ((size >> PAGE_SHIFT) != (1ul << (region_width - 11))) { - /* not pow2, so must go up to the next pow2 */ - region_width += 1; - } + /* The size is encoded as ceil(log2) minus(1), which may be calculated + * with fls. The size must be clamped to hardware bounds. + */ + size = max_t(u64, size, PAGE_SIZE); + region_width = fls64(size - 1) - 1; region |= region_width; /* Lock the region that needs to be updated */