Re: [PATCH 1/1] lib/ioremap.c: avoid endless loop under ioremapping page unaligned ranges
From: Michal Hocko <mhocko@kernel.org>
Date: 2016-09-22 12:47:42
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On Wed 21-09-16 12:19:53, zijun_hu wrote:
From: zijun_hu <redacted> endless loop maybe happen if either of parameter addr and end is not page aligned for kernel API function ioremap_page_range()
Does this happen in practise or this you found it by reading the code?
quoted hunk ↗ jump to hunk
in order to fix this issue and alert improper range parameters to user WARN_ON() checkup and rounding down range lower boundary are performed firstly, loop end condition within ioremap_pte_range() is optimized due to lack of relevant macro pte_addr_end() Signed-off-by: zijun_hu <redacted> --- lib/ioremap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/lib/ioremap.c b/lib/ioremap.c index 86c8911..911bdca 100644 --- a/lib/ioremap.c +++ b/lib/ioremap.c@@ -64,7 +64,7 @@ static int ioremap_pte_range(pmd_t *pmd, unsigned long addr, BUG_ON(!pte_none(*pte)); set_pte_at(&init_mm, addr, pte, pfn_pte(pfn, prot)); pfn++; - } while (pte++, addr += PAGE_SIZE, addr != end); + } while (pte++, addr += PAGE_SIZE, addr < end && addr >= PAGE_SIZE); return 0; }
Ble, this just overcomplicate things. Can we just make sure that the proper alignment is done in ioremap_page_range which is the only caller of this (and add VM_BUG_ON in ioremap_pud_range to make sure no new caller will forget about that).
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@@ -129,7 +129,9 @@ int ioremap_page_range(unsigned long addr, int err; BUG_ON(addr >= end); + WARN_ON(!PAGE_ALIGNED(addr) || !PAGE_ALIGNED(end));
maybe WARN_ON_ONCE would be sufficient to prevent from swamping logs if something just happens to do this too often in some pathological path.
+ addr = round_down(addr, PAGE_SIZE);
end = round_up(end, PAGE_SIZE); wouldn't work?
start = addr; phys_addr -= addr; pgd = pgd_offset_k(addr); -- 1.9.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
-- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>