This is a note to let you know that I've just added the patch titled
x86/CPU/AMD: Do not leak quotient data after a division by 0
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-cpu-amd-do-not-leak-quotient-data-after-a-division-by-0.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 77245f1c3c6495521f6a3af082696ee2f8ce3921 Mon Sep 17 00:00:00 2001
From: "Borislav Petkov (AMD)" <bp@xxxxxxxxx>
Date: Sat, 5 Aug 2023 00:06:43 +0200
Subject: x86/CPU/AMD: Do not leak quotient data after a division by 0
From: Borislav Petkov (AMD) <bp@xxxxxxxxx>
commit 77245f1c3c6495521f6a3af082696ee2f8ce3921 upstream.
Under certain circumstances, an integer division by 0 which faults, can
leave stale quotient data from a previous division operation on Zen1
microarchitectures.
Do a dummy division 0/1 before returning from the #DE exception handler
in order to avoid any leaks of potentially sensitive data.
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/processor.h | 2 ++
arch/x86/kernel/cpu/amd.c | 19 +++++++++++++++++++
arch/x86/kernel/traps.c | 2 ++
4 files changed, 24 insertions(+)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -495,4 +495,5 @@
/* BUG word 2 */
#define X86_BUG_SRSO X86_BUG(1*32 + 0) /* AMD SRSO bug */
+#define X86_BUG_DIV0 X86_BUG(1*32 + 1) /* AMD DIV0 speculation bug */
#endif /* _ASM_X86_CPUFEATURES_H */
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -684,10 +684,12 @@ extern u16 get_llc_id(unsigned int cpu);
extern u32 amd_get_nodes_per_socket(void);
extern u32 amd_get_highest_perf(void);
extern bool cpu_has_ibpb_brtype_microcode(void);
+extern void amd_clear_divider(void);
#else
static inline u32 amd_get_nodes_per_socket(void) { return 0; }
static inline u32 amd_get_highest_perf(void) { return 0; }
static inline bool cpu_has_ibpb_brtype_microcode(void) { return false; }
+static inline void amd_clear_divider(void) { }
#endif
extern unsigned long arch_align_stack(unsigned long sp);
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -75,6 +75,10 @@ static const int amd_zenbleed[] =
AMD_MODEL_RANGE(0x17, 0x60, 0x0, 0x7f, 0xf),
AMD_MODEL_RANGE(0x17, 0xa0, 0x0, 0xaf, 0xf));
+static const int amd_div0[] =
+ AMD_LEGACY_ERRATUM(AMD_MODEL_RANGE(0x17, 0x00, 0x0, 0x2f, 0xf),
+ AMD_MODEL_RANGE(0x17, 0x50, 0x0, 0x5f, 0xf));
+
static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum)
{
int osvw_id = *erratum++;
@@ -1130,6 +1134,11 @@ static void init_amd(struct cpuinfo_x86
WARN_ON_ONCE(msr_set_bit(MSR_EFER, _EFER_AUTOIBRS));
zenbleed_check(c);
+
+ if (cpu_has_amd_erratum(c, amd_div0)) {
+ pr_notice_once("AMD Zen1 DIV0 bug detected. Disable SMT for full protection.\n");
+ setup_force_cpu_bug(X86_BUG_DIV0);
+ }
}
#ifdef CONFIG_X86_32
@@ -1309,3 +1318,13 @@ void amd_check_microcode(void)
{
on_each_cpu(zenbleed_check_cpu, NULL, 1);
}
+
+/*
+ * Issue a DIV 0/1 insn to clear any division data from previous DIV
+ * operations.
+ */
+void noinstr amd_clear_divider(void)
+{
+ asm volatile(ALTERNATIVE("", "div %2\n\t", X86_BUG_DIV0)
+ :: "a" (0), "d" (0), "r" (1));
+}
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -206,6 +206,8 @@ 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)
Patches currently in stable-queue which might be from bp@xxxxxxxxx are
queue-6.4/x86-cpu-amd-do-not-leak-quotient-data-after-a-division-by-0.patch
