On Sat, Apr 10, 2021 at 07:51:58AM -0700, Andy Lutomirski wrote: > Can you add STAR, CSTAR, LSTAR, SYSENTER*, SYSCALL*, and EFER please?
Sure. --- From: Borislav Petkov <b...@suse.de> Date: Sat, 10 Apr 2021 14:08:13 +0200 There are a bunch of MSRs which luserspace has no business poking at, whatsoever. Add a ban list and put the TSC-related MSRs and the ring0-entry and features control MSRs in there. Issue a big juicy splat to catch offenders. Signed-off-by: Borislav Petkov <b...@suse.de> --- arch/x86/kernel/msr.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index ed8ac6bcbafb..2435a619cd9f 100644 --- a/arch/x86/kernel/msr.c +++ b/arch/x86/kernel/msr.c @@ -78,6 +78,21 @@ static ssize_t msr_read(struct file *file, char __user *buf, return bytes ? bytes : err; } +static const u32 msr_ban_list[] = { + MSR_IA32_TSC, + MSR_TSC_AUX, + MSR_IA32_TSC_ADJUST, + MSR_IA32_TSC_DEADLINE, + MSR_EFER, + MSR_STAR, + MSR_CSTAR, + MSR_LSTAR, + MSR_SYSCALL_MASK, + MSR_IA32_SYSENTER_CS, + MSR_IA32_SYSENTER_ESP, + MSR_IA32_SYSENTER_EIP, +}; + static int filter_write(u32 reg) { /* @@ -89,6 +104,16 @@ static int filter_write(u32 reg) * avoid saturating the ring buffer. */ static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1); + int i; + + for (i = 0; i < ARRAY_SIZE(msr_ban_list); i++) { + if (msr_ban_list[i] != reg) + continue; + + WARN_ONCE(1, "Blocked write to MSR 0x%x.\n", reg); + + return -EINVAL; + } switch (allow_writes) { case MSR_WRITES_ON: return 0; -- 2.29.2 -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette