Re: [RFC PATCH 09/12] drivers: hv: hv_vsm_boot: Enable VTL1 on the boot processor

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

New issues:
- [High] Unconditional loading of the secure kernel overwrites VTL1 memory even if VTL1 is already active, leading to memory corruption or fatal faults.

Pre-existing issues:
- [High] Missing bounds check when parsing ELF program headers from firmware, leading to potential out-of-bounds read.
--

commit 58f06b8de69e2f750e55a8ff7220ab38d88c0f8f
Author: Thara Gopinath <tgopinath@linux.microsoft.com>

drivers: hv: hv_vsm_boot: Enable VTL1 on the boot processor

This commit introduces helpers to get VP status and enable VTL1 on the boot
virtual processor. It extends hv_vsm_bootstrap_vtl() to enable VTL1 on the
boot VP if it is not already enabled, and re-queries the status to confirm
the transition.

> diff --git a/drivers/hv/hv_vsm_boot.c b/drivers/hv/hv_vsm_boot.c
> index dc20f935da5b2..abe82e03e1897 100644
> --- a/drivers/hv/hv_vsm_boot.c
> +++ b/drivers/hv/hv_vsm_boot.c
> @@ -216,6 +216,47 @@ static int __init hv_vsm_load_secure_kernel(Elf64_Addr *sk_entry_pa)
>  	return ret;
>  }

[Severity: High]
This isn't a bug introduced by this patch, but there appears to be a missing
bounds check when parsing ELF program headers from the firmware in
hv_vsm_load_elf() which is called by hv_vsm_load_secure_kernel().

The firmware size (fw->size) is discarded instead of being passed to
hv_vsm_load_elf() for validation. Inside hv_vsm_load_elf(), the program header
table offset (e_phoff) is never bounds-checked against the firmware size before
being iterated over:

drivers/hv/hv_vsm_boot.c:hv_vsm_load_elf() {
    ...
    Elf64_Phdr *phdr = image + ehdr->e_phoff;
    ...
}

Later, the memcpy() copies uncontrolled lengths of kernel memory based on
untrusted firmware headers:

drivers/hv/hv_vsm_boot.c:hv_vsm_load_elf() {
    ...
    memcpy(load_addr, image + phdr->p_offset, phdr->p_filesz);
    ...
}

Could a malformed or maliciously crafted firmware file cause an out-of-bounds
read past the end of the firmware buffer, potentially leaking sensitive kernel
data into the secure kernel's memory or causing a kernel panic?

[ ... ]

> @@ -300,7 +342,34 @@ static int __init hv_vsm_bootstrap_vtl(void)
>  		}
>  	}
>  
> -	return hv_vsm_load_secure_kernel(&sk_entry_pa);
> +	ret = hv_vsm_load_secure_kernel(&sk_entry_pa);
> +	if (ret)
> +		return ret;
> +
> +	/* Check and enable VTL1 for the primary virtual processor */
> +	ret = hv_vsm_get_vp_status(&vp_enabled_vtl_set, &active_mbec_enabled);
> +	if (ret)
> +		return ret;
> +
> +	if (vp_enabled_vtl_set & HV_VTL1_ENABLE_BIT) {
> +		pr_info("VP VTL1 is already enabled\n");

[Severity: High]
If VTL1 is already enabled, does calling hv_vsm_load_secure_kernel() earlier
in this function overwrite the memory of the currently running VTL1 secure
kernel?

Since hv_vsm_load_secure_kernel() is called unconditionally before checking if
VP VTL1 is active, could unconditionally loading the secure kernel ELF image
cause a regression by triggering a fatal hypervisor intercept/fault in VTL0,
or silently corrupting the active VTL1 (such as during a kexec reboot)?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260901165647.3160413-1-tgopinath@linux.microsoft.com?part=9