From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: tglx@linutronix.de, bp@suse.de, hpa@zytor.com,
linux-kernel@vger.kernel.org, mingo@redhat.com, x86@kernel.org,
mingo@kernel.org, kirill.shutemov@linux.intel.com,
kirill@shutemov.name, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/boot/compressed/64: Fix boot on machines with broken E820 table
Date: Sun, 25 Aug 2019 22:33:15 -0500 [thread overview]
Message-ID: <caa30daa-9ed5-e293-f6cd-ff261c995e1e@embeddedor.com> (raw)
In-Reply-To: <tip-0a46fff2f9108c2c44218380a43a736cf4612541@git.kernel.org>
Hi all,
On 8/19/19 9:16 AM, tip-bot for Kirill A. Shutemov wrote:
[..]
>
> 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)
Notice that if this condition happens to be false, we end up with an
uninitialized variable *new*.
What would be the right value to assign to *new* at declaration under
this condition?
> - 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;
> }
>
>
--
Gustavo
next prev parent reply other threads:[~2019-08-26 3:37 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:x86/urgent] " tip-bot for Kirill A. Shutemov
2019-08-26 3:33 ` Gustavo A. R. Silva [this message]
2019-08-26 7:15 ` Borislav Petkov
2019-08-26 13:33 ` Kirill A. Shutemov
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