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x86/mm: Handle decryption/re-encryption of bss_decrypted consistently

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sme_postprocess_startup() decrypts the bss_decrypted section when
sme_me_mask is non-zero.

mem_encrypt_free_decrypted_mem() re-encrypts the unused portion based
on CC_ATTR_MEM_ENCRYPT.

In a Hyper-V guest VM using vTOM, these conditions are not equivalent
as sme_me_mask is always zero when using vTOM. Consequently,
mem_encrypt_free_decrypted_mem() attempts to re-encrypt memory that was
never decrypted.

So check sme_me_mask in mem_encrypt_free_decrypted_mem() too.

Hyper-V guests using vTOM don't need the bss_decrypted section to be
decrypted, so skipping the decryption/re-encryption doesn't cause a
problem.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/1678329614-3482-5-git-send-email-mikelley@microsoft.com
This commit is contained in:
Michael Kelley 2023-03-08 18:40:05 -08:00 committed by Borislav Petkov (AMD)
parent d33ddc92db
commit c7b5254bd8
1 changed files with 7 additions and 3 deletions
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10
arch/x86/mm/mem_encrypt_amd.c
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@ -513,10 +513,14 @@ void __init mem_encrypt_free_decrypted_mem(void)
npages = (vaddr_end - vaddr) >> PAGE_SHIFT;
/*
* The unused memory range was mapped decrypted, change the encryption
* attribute from decrypted to encrypted before freeing it.
* If the unused memory range was mapped decrypted, change the encryption
* attribute from decrypted to encrypted before freeing it. Base the
* re-encryption on the same condition used for the decryption in
* sme_postprocess_startup(). Higher level abstractions, such as
* CC_ATTR_MEM_ENCRYPT, aren't necessarily equivalent in a Hyper-V VM
* using vTOM, where sme_me_mask is always zero.
*/
if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
if (sme_me_mask) {
r = set_memory_encrypted(vaddr, npages);
if (r) {
pr_warn("failed to free unused decrypted pages\n");