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Re: [PATCH 2/3] x86/boot: Fix microcode module handling during PVH boot
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 23 Oct 2024 08:17:12 -0400
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 23 Oct 2024 12:17:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/23/24 06:57, Andrew Cooper wrote:
From: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
As detailed in commit 0fe607b2a144 ("x86/boot: Fix PVH boot during boot_info
transition period"), the use of __va(mbi->mods_addr) constitutes a
use-after-free on the PVH boot path.
This pattern has been in use since before PVH support was added. Inside a PVH
VM, it will go unnoticed as long as the microcode container parser doesn't
choke on the random data it finds.
The use within early_microcode_init() happens to be safe because it's prior to
move_xen(). microcode_init_cache() is after move_xen(), and therefore unsafe.
Plumb the boot_info pointer down, replacing module_map and mbi. Importantly,
bi->mods[].mod is a safe way to access the module list during PVH boot.
Note: microcode_scan_module() is still bogusly stashing a bootstrap_map()'d
pointer in ucode_blob.data, which constitutes a different
use-after-free, and only works in general because of a second bug. This
is unrelated to PVH, and needs untangling differently.
Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
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