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Date: Tue, 25 Jun 2019 21:56:56 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: "Kirill A. Shutemov" <kirill@...temov.name> cc: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, linux-kernel@...r.kernel.org, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> Subject: Re: [PATCH] x86/boot/64: Fix crash if kernel images crosses page table boundary On Tue, 25 Jun 2019, Kirill A. Shutemov wrote: > On Tue, Jun 25, 2019 at 09:04:39PM +0200, Thomas Gleixner wrote: > > > > + pmd[idx % PTRS_PER_PMD] = pmd_entry + i * PMD_SIZE; > > > > This part is functionally equivivalent. So what's the value of this change? > > Precedence of operators were broken > > idx = i + (physaddr >> PMD_SHIFT) % PTRS_PER_PMD; > > reads by compiler as > > idx = i + ((physaddr >> PMD_SHIFT) % PTRS_PER_PMD); > > not as > > idx = (i + (physaddr >> PMD_SHIFT)) % PTRS_PER_PMD; > > Therefore 'idx' can become >= PTRS_PER_PMD. Indeed. Please mention it in the change log. I did not spot it right away. Thanks, tglx
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