linux-kernel - [PATCH 3/3] x86/kexec: Allocate 8k PGDs for PTI

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Date:   Wed, 25 Jul 2018 17:48:03 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>,
        jroedel@...e.de, Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>, joro@...tes.org
Subject: [PATCH 3/3] x86/kexec: Allocate 8k PGDs for PTI

From: Joerg Roedel <jroedel@...e.de>

Fuzzing the PTI-x86-32 code with trinity showed unhandled
kernel paging request oops-messages that looked a lot like
silent data corruption.

Lot's of debugging and testing lead to the kexec-32bit code,
which is still allocating 4k PGDs when PTI is enabled. But
since it uses native_set_pud() to build the page-table, it
will unevitably call into __pti_set_user_pgtbl(), which
writes beyond the allocated 4k page.

Use PGD_ALLOCATION_ORDER to allocate PGDs in the kexec code
to fix the issue.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/machine_kexec_32.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_32.c b/arch/x86/kernel/machine_kexec_32.c
index d1ab07e..5409c28 100644
--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -56,7 +56,7 @@ static void load_segments(void)
 
 static void machine_kexec_free_page_tables(struct kimage *image)
 {
-	free_page((unsigned long)image->arch.pgd);
+	free_pages((unsigned long)image->arch.pgd, PGD_ALLOCATION_ORDER);
 	image->arch.pgd = NULL;
 #ifdef CONFIG_X86_PAE
 	free_page((unsigned long)image->arch.pmd0);
@@ -72,7 +72,8 @@ static void machine_kexec_free_page_tables(struct kimage *image)
 
 static int machine_kexec_alloc_page_tables(struct kimage *image)
 {
-	image->arch.pgd = (pgd_t *)get_zeroed_page(GFP_KERNEL);
+	image->arch.pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+						    PGD_ALLOCATION_ORDER);
 #ifdef CONFIG_X86_PAE
 	image->arch.pmd0 = (pmd_t *)get_zeroed_page(GFP_KERNEL);
 	image->arch.pmd1 = (pmd_t *)get_zeroed_page(GFP_KERNEL);
-- 
2.7.4