5.15-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 41e71dbb0e0a0fe214545fe64af031303a08524c ]
Guenter reported dodgy crashes on an i386-nosmp build using GCC-11 that had the form of endless traps until entry stack exhaust and then #DF from the stack guard.
It turned out that pti_clone_pgtable() had alignment assumptions on the start address, notably it hard assumes start is PMD aligned. This is true on x86_64, but very much not true on i386.
These assumptions can cause the end condition to malfunction, leading to a 'short' clone. Guess what happens when the user mapping has a short copy of the entry text?
Use the correct increment form for addr to avoid alignment assumptions.
Fixes: 16a3fe634f6a ("x86/mm/pti: Clone kernel-image on PTE level for 32 bit") Reported-by: Guenter Roeck linux@roeck-us.net Tested-by: Guenter Roeck linux@roeck-us.net Suggested-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20240731163105.GG33588@noisy.programming.kicks-ass... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/mm/pti.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index 5d5c7bb50ce9e..c11c808eeac26 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -374,14 +374,14 @@ pti_clone_pgtable(unsigned long start, unsigned long end, */ *target_pmd = *pmd;
- addr += PMD_SIZE; + addr = round_up(addr + 1, PMD_SIZE);
} else if (level == PTI_CLONE_PTE) {
/* Walk the page-table down to the pte level */ pte = pte_offset_kernel(pmd, addr); if (pte_none(*pte)) { - addr += PAGE_SIZE; + addr = round_up(addr + 1, PAGE_SIZE); continue; }
@@ -401,7 +401,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end, /* Clone the PTE */ *target_pte = *pte;
- addr += PAGE_SIZE; + addr = round_up(addr + 1, PAGE_SIZE);
} else { BUG();