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Subject[tip: x86/pti] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()
The following commit has been merged into the x86/pti branch of tip:

Commit-ID: 825d0b73cd7526b0bb186798583fae810091cbac
Gitweb: https://git.kernel.org/tip/825d0b73cd7526b0bb186798583fae810091cbac
Author: Song Liu <songliubraving@fb.com>
AuthorDate: Wed, 28 Aug 2019 23:54:55 +02:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 29 Aug 2019 20:52:52 +02:00

x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()

pti_clone_pmds() assumes that the supplied address is either:

- properly PUD/PMD aligned
or
- the address is actually mapped which means that independently
of the mapping level (PUD/PMD/PTE) the next higher mapping
exists.

If that's not the case the unaligned address can be incremented by PUD or
PMD size incorrectly. All callers supply mapped and/or aligned addresses,
but for the sake of robustness it's better to handle that case properly and
to emit a warning.

[ tglx: Rewrote changelog and added WARN_ON_ONCE() ]

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908282352470.1938@nanos.tec.linutronix.de

---
arch/x86/mm/pti.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b196524..a24487b 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -330,13 +330,15 @@ pti_clone_pgtable(unsigned long start, unsigned long end,

pud = pud_offset(p4d, addr);
if (pud_none(*pud)) {
- addr += PUD_SIZE;
+ WARN_ON_ONCE(addr & ~PUD_MASK);
+ addr = round_up(addr + 1, PUD_SIZE);
continue;
}

pmd = pmd_offset(pud, addr);
if (pmd_none(*pmd)) {
- addr += PMD_SIZE;
+ WARN_ON_ONCE(addr & ~PMD_MASK);
+ addr = round_up(addr + 1, PMD_SIZE);
continue;
}

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