Commit f58d6fbc authored by Borislav Petkov (AMD)'s avatar Borislav Petkov (AMD)
Browse files

x86/CPU/AMD: Fix the DIV(0) initial fix attempt 



Initially, it was thought that doing an innocuous division in the #DE
handler would take care to prevent any leaking of old data from the
divider but by the time the fault is raised, the speculation has already
advanced too far and such data could already have been used by younger
operations.

Therefore, do the innocuous division on every exit to userspace so that
userspace doesn't see any potentially old data from integer divisions in
kernel space.

Do the same before VMRUN too, to protect host data from leaking into the
guest too.

Fixes: 77245f1c ("x86/CPU/AMD: Do not leak quotient data after a division by 0")
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@alien8.de
parent ba5ca5e5

arch/x86/include/asm/entry-common.h

+1 −0
Original line number Diff line number Diff line
@@ -92,6 +92,7 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, 
static __always_inline void arch_exit_to_user_mode(void)

{

	mds_user_clear_cpu_buffers();

	amd_clear_divider();

}

#define arch_exit_to_user_mode arch_exit_to_user_mode

arch/x86/kernel/cpu/amd.c

+1 −0
Original line number Diff line number Diff line
@@ -1329,3 +1329,4 @@ void noinstr amd_clear_divider(void) 
	asm volatile(ALTERNATIVE("", "div %2\n\t", X86_BUG_DIV0)

		     :: "a" (0), "d" (0), "r" (1));

}

EXPORT_SYMBOL_GPL(amd_clear_divider);

arch/x86/kernel/traps.c

+0 −2
Original line number Diff line number Diff line
@@ -206,8 +206,6 @@ DEFINE_IDTENTRY(exc_divide_error) 
{

	do_error_trap(regs, 0, "divide error", X86_TRAP_DE, SIGFPE,

		      FPE_INTDIV, error_get_trap_addr(regs));



	amd_clear_divider();

}



DEFINE_IDTENTRY(exc_overflow)

arch/x86/kvm/svm/svm.c

+2 −0
Original line number Diff line number Diff line
@@ -4006,6 +4006,8 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_in 


	guest_state_enter_irqoff();



	amd_clear_divider();



	if (sev_es_guest(vcpu->kvm))

		__svm_sev_es_vcpu_run(svm, spec_ctrl_intercepted);

	else