From: Ard Biesheuvel ardb@kernel.org
[ Upstream commit e814b59e6c2b11f5a3d007b2e61f7d550c354c3a ]
Commit
cbebd68f59f0 ("x86/mm: Fix use of uninitialized buffer in sme_enable()")
'fixed' an issue in sme_enable() detected by static analysis, and broke the common case in the process.
cmdline_find_option() will return < 0 on an error, or when the command line argument does not appear at all. In this particular case, the latter is not an error condition, and so the early exit is wrong.
Instead, without mem_encrypt= on the command line, the compile time default should be honoured, which could be to enable memory encryption, and this is currently broken.
Fix it by setting sme_me_mask to a preliminary value based on the compile time default, and only omitting the command line argument test when cmdline_find_option() returns an error.
[ bp: Drop active_by_default while at it. ]
Fixes: cbebd68f59f0 ("x86/mm: Fix use of uninitialized buffer in sme_enable()") Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Reviewed-by: Tom Lendacky thomas.lendacky@amd.com Link: https://lore.kernel.org/r/20240126163918.2908990-2-ardb+git@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/mm/mem_encrypt_identity.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c index d94ebd8acdfde..a11a6ebbf5ecf 100644 --- a/arch/x86/mm/mem_encrypt_identity.c +++ b/arch/x86/mm/mem_encrypt_identity.c @@ -507,7 +507,6 @@ void __init sme_enable(struct boot_params *bp) const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off; unsigned int eax, ebx, ecx, edx; unsigned long feature_mask; - bool active_by_default; unsigned long me_mask; char buffer[16]; bool snp; @@ -593,22 +592,19 @@ void __init sme_enable(struct boot_params *bp) : "p" (sme_cmdline_off));
if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT)) - active_by_default = true; - else - active_by_default = false; + sme_me_mask = me_mask;
cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr | ((u64)bp->ext_cmd_line_ptr << 32));
if (cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer)) < 0) - return; + goto out;
if (!strncmp(buffer, cmdline_on, sizeof(buffer))) sme_me_mask = me_mask; else if (!strncmp(buffer, cmdline_off, sizeof(buffer))) sme_me_mask = 0; - else - sme_me_mask = active_by_default ? me_mask : 0; + out: if (sme_me_mask) { physical_mask &= ~sme_me_mask;