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

commit f58d6fbcb7c848b7f2469be339bc571f2e9d245b upstream.

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: 77245f1c3c64 ("x86/CPU/AMD: Do not leak quotient data after a division by 0")
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@alien8.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 4a382fb6a9ef88b4e2a7cc3efe2464837d3ec1c6..5443851d3aa6089e592ee60b0fb30120c1e1ac4d 100644 (file)
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -78,6 +78,7 @@ 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
 

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 7f351093cd947810b9c4eaabc022923d001b0fc4..2bc1c78a7cc574cab873f48b812c4e1f54a89de7 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1332,3 +1332,4 @@ 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);

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 28f5cc0a9decbe98fbcf6654da7cf71dd8cc7c15..98838b784524e7710d091a367c902c89feee09b1 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -198,8 +198,6 @@ 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)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 8544bca6b33568e16ad4d6979418b57ef4b0e6aa..1616e39ddc3f16a270185b6972ec86a891f3fa0b 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3376,6 +3376,7 @@ static void svm_flush_tlb_gva(struct kvm_vcpu *vcpu, gva_t gva)
 
 static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
 {
+       amd_clear_divider();
 }
 
 static inline void sync_cr8_to_lapic(struct kvm_vcpu *vcpu)