The following commit has been merged into the x86/seves branch of tip: Commit-ID: c9f09539e16e281f92a27760fdfae71e8af036f6 Gitweb: https://git.kernel.org/tip/c9f09539e16e281f92a27760fdfae71e8af036f6 Author: Joerg Roedel <jroe...@suse.de> AuthorDate: Wed, 28 Oct 2020 17:46:58 +01:00 Committer: Borislav Petkov <b...@suse.de> CommitterDate: Thu, 29 Oct 2020 18:09:59 +01:00
x86/head/64: Check SEV encryption before switching to kernel page-table When SEV is enabled, the kernel requests the C-bit position again from the hypervisor to build its own page-table. Since the hypervisor is an untrusted source, the C-bit position needs to be verified before the kernel page-table is used. Call sev_verify_cbit() before writing the CR3. [ bp: Massage. ] Signed-off-by: Joerg Roedel <jroe...@suse.de> Signed-off-by: Borislav Petkov <b...@suse.de> Reviewed-by: Tom Lendacky <thomas.lenda...@amd.com> Link: https://lkml.kernel.org/r/20201028164659.27002-5-j...@8bytes.org --- arch/x86/kernel/head_64.S | 16 ++++++++++++++++ arch/x86/mm/mem_encrypt.c | 1 + 2 files changed, 17 insertions(+) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 7eb2a1c..3c41773 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -161,6 +161,21 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) /* Setup early boot stage 4-/5-level pagetables. */ addq phys_base(%rip), %rax + + /* + * For SEV guests: Verify that the C-bit is correct. A malicious + * hypervisor could lie about the C-bit position to perform a ROP + * attack on the guest by writing to the unencrypted stack and wait for + * the next RET instruction. + * %rsi carries pointer to realmode data and is callee-clobbered. Save + * and restore it. + */ + pushq %rsi + movq %rax, %rdi + call sev_verify_cbit + popq %rsi + + /* Switch to new page-table */ movq %rax, %cr3 /* Ensure I am executing from virtual addresses */ @@ -279,6 +294,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) SYM_CODE_END(secondary_startup_64) #include "verify_cpu.S" +#include "sev_verify_cbit.S" #ifdef CONFIG_HOTPLUG_CPU /* diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c index efbb3de..bc08337 100644 --- a/arch/x86/mm/mem_encrypt.c +++ b/arch/x86/mm/mem_encrypt.c @@ -39,6 +39,7 @@ */ u64 sme_me_mask __section(".data") = 0; u64 sev_status __section(".data") = 0; +u64 sev_check_data __section(".data") = 0; EXPORT_SYMBOL(sme_me_mask); DEFINE_STATIC_KEY_FALSE(sev_enable_key); EXPORT_SYMBOL_GPL(sev_enable_key);
