From: Kairui Song kasong@redhat.com
[ Upstream commit bdec8d7fa55e6f5314ed72e5a0b435d90ff90548 ]
Commit
1958b5fc4010 ("x86/boot: Add early boot support when running with SEV active")
can occasionally cause system resets when kexec-ing a second kernel even if SEV is not active.
That's because get_sev_encryption_bit() uses 32-bit rIP-relative addressing to read the value of enc_bit - a variable which caches a previously detected encryption bit position - but kexec may allocate the early boot code to a higher location, beyond the 32-bit addressing limit.
In this case, garbage will be read and get_sev_encryption_bit() will return the wrong value, leading to accessing memory with the wrong encryption setting.
Therefore, remove enc_bit, and thus get rid of the need to do 32-bit rIP-relative addressing in the first place.
[ bp: massage commit message heavily. ]
Fixes: 1958b5fc4010 ("x86/boot: Add early boot support when running with SEV active") Suggested-by: Borislav Petkov bp@suse.de Signed-off-by: Kairui Song kasong@redhat.com Signed-off-by: Borislav Petkov bp@suse.de Reviewed-by: Tom Lendacky thomas.lendacky@amd.com Cc: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de Cc: mingo@redhat.com Cc: hpa@zytor.com Cc: brijesh.singh@amd.com Cc: kexec@lists.infradead.org Cc: dyoung@redhat.com Cc: bhe@redhat.com Cc: ghook@redhat.com Link: https://lkml.kernel.org/r/20180927123845.32052-1-kasong@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/x86/boot/compressed/mem_encrypt.S | 19 ------------------- 1 file changed, 19 deletions(-)
diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S index eaa843a52907..a480356e0ed8 100644 --- a/arch/x86/boot/compressed/mem_encrypt.S +++ b/arch/x86/boot/compressed/mem_encrypt.S @@ -25,20 +25,6 @@ ENTRY(get_sev_encryption_bit) push %ebx push %ecx push %edx - push %edi - - /* - * RIP-relative addressing is needed to access the encryption bit - * variable. Since we are running in 32-bit mode we need this call/pop - * sequence to get the proper relative addressing. - */ - call 1f -1: popl %edi - subl $1b, %edi - - movl enc_bit(%edi), %eax - cmpl $0, %eax - jge .Lsev_exit
/* Check if running under a hypervisor */ movl $1, %eax @@ -69,15 +55,12 @@ ENTRY(get_sev_encryption_bit)
movl %ebx, %eax andl $0x3f, %eax /* Return the encryption bit location */ - movl %eax, enc_bit(%edi) jmp .Lsev_exit
.Lno_sev: xor %eax, %eax - movl %eax, enc_bit(%edi)
.Lsev_exit: - pop %edi pop %edx pop %ecx pop %ebx @@ -113,8 +96,6 @@ ENTRY(set_sev_encryption_mask) ENDPROC(set_sev_encryption_mask)
.data -enc_bit: - .int 0xffffffff
#ifdef CONFIG_AMD_MEM_ENCRYPT .balign 8