From: "tip-bot for Kirill A. Shutemov" <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: mingo@kernel.org, kirill.shutemov@linux.intel.com,
x86@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org,
bp@suse.de, hpa@zytor.com, tglx@linutronix.de,
kirill@shutemov.name
Subject: [tip:x86/urgent] x86/boot/compressed/64: Fix boot on machines with broken E820 table
Date: Mon, 19 Aug 2019 07:16:04 -0700 [thread overview]
Message-ID: <tip-0a46fff2f9108c2c44218380a43a736cf4612541@git.kernel.org> (raw)
In-Reply-To: <20190813131654.24378-1-kirill.shutemov@linux.intel.com>
Commit-ID: 0a46fff2f9108c2c44218380a43a736cf4612541
Gitweb: https://git.kernel.org/tip/0a46fff2f9108c2c44218380a43a736cf4612541
Author: Kirill A. Shutemov <kirill@shutemov.name>
AuthorDate: Tue, 13 Aug 2019 16:16:54 +0300
Committer: Borislav Petkov <bp@suse.de>
CommitDate: Mon, 19 Aug 2019 15:59:13 +0200
x86/boot/compressed/64: Fix boot on machines with broken E820 table
BIOS on Samsung 500C Chromebook reports very rudimentary E820 table that
consists of 2 entries:
BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] usable
BIOS-e820: [mem 0x00000000fffff000-0x00000000ffffffff] reserved
It breaks logic in find_trampoline_placement(): bios_start lands on the
end of the first 4k page and trampoline start gets placed below 0.
Detect underflow and don't touch bios_start for such cases. It makes
kernel ignore E820 table on machines that doesn't have two usable pages
below BIOS_START_MAX.
Fixes: 1b3a62643660 ("x86/boot/compressed/64: Validate trampoline placement against E820")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=203463
Link: https://lkml.kernel.org/r/20190813131654.24378-1-kirill.shutemov@linux.intel.com
---
arch/x86/boot/compressed/pgtable_64.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 5f2d03067ae5..2faddeb0398a 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -72,6 +72,8 @@ static unsigned long find_trampoline_placement(void)
/* Find the first usable memory region under bios_start. */
for (i = boot_params->e820_entries - 1; i >= 0; i--) {
+ unsigned long new;
+
entry = &boot_params->e820_table[i];
/* Skip all entries above bios_start. */
@@ -84,15 +86,20 @@ static unsigned long find_trampoline_placement(void)
/* Adjust bios_start to the end of the entry if needed. */
if (bios_start > entry->addr + entry->size)
- bios_start = entry->addr + entry->size;
+ new = entry->addr + entry->size;
/* Keep bios_start page-aligned. */
- bios_start = round_down(bios_start, PAGE_SIZE);
+ new = round_down(new, PAGE_SIZE);
/* Skip the entry if it's too small. */
- if (bios_start - TRAMPOLINE_32BIT_SIZE < entry->addr)
+ if (new - TRAMPOLINE_32BIT_SIZE < entry->addr)
continue;
+ /* Protect against underflow. */
+ if (new - TRAMPOLINE_32BIT_SIZE > bios_start)
+ break;
+
+ bios_start = new;
break;
}
next prev parent reply other threads:[~2019-08-19 14:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 13:16 [PATCH] x86/boot/compressed/64: Fix boot on machines with broken E820 table Kirill A. Shutemov
2019-08-19 14:16 ` tip-bot for Kirill A. Shutemov [this message]
2019-08-26 3:33 ` [tip:x86/urgent] " Gustavo A. R. Silva
2019-08-26 7:15 ` Borislav Petkov
2019-08-26 13:33 ` Kirill A. Shutemov
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