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vmm: avoid potential KASSERT kernel panic in vm_handle_db

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If the guest VM emits the exit code VM_EXITCODE_DB the kernel will
execute the function named vm_handle_db.

If the value of rsp is not page aligned and if rsp+sizeof(uint64_t)
spans across two pages, the function vm_copy_setup will need two structs
vm_copyinfo to prepare the copy operation.

For instance is rsp value is 0xFFC, two vm_copyinfo objects are needed:

* address=0xFFC, len=4
* address=0x1000, len=4

The vulnerability was addressed by commit 51fda658ba ("vmm: Properly
handle writes spanning across two pages in vm_handle_db").  Still,
replace the KASSERT with an error return as a more defensive approach.

Reported by:    Synacktiv
Reviewed by	markj, emaste
Security:       HYP-09
Sponsored by:   The Alpha-Omega Project
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D46133
This commit is contained in:
Pierre Pronchery 2024-07-25 16:40:35 +02:00 committed by Ed Maste
parent 51fda658ba
commit d19fa9c1b7
1 changed files with 2 additions and 1 deletions
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3
sys/amd64/vmm/vmm.c
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@ -2810,7 +2810,8 @@ vm_copy_setup(struct vcpu *vcpu, struct vm_guest_paging *paging,
nused = 0;
remaining = len;
while (remaining > 0) {
KASSERT(nused < num_copyinfo, ("insufficient vm_copyinfo"));
if (nused >= num_copyinfo)
return (EFAULT);
error = vm_gla2gpa(vcpu, paging, gla, prot, &gpa, fault);
if (error || *fault)
return (error);