| From foo@baz Thu Feb 8 03:32:24 CET 2018 |
| From: Dan Williams <dan.j.williams@intel.com> |
| Date: Mon, 29 Jan 2018 17:02:59 -0800 |
| Subject: x86/syscall: Sanitize syscall table de-references under speculation |
| |
| From: Dan Williams <dan.j.williams@intel.com> |
| |
| |
| (cherry picked from commit 2fbd7af5af8665d18bcefae3e9700be07e22b681) |
| |
| The syscall table base is a user controlled function pointer in kernel |
| space. Use array_index_nospec() to prevent any out of bounds speculation. |
| |
| While retpoline prevents speculating into a userspace directed target it |
| does not stop the pointer de-reference, the concern is leaking memory |
| relative to the syscall table base, by observing instruction cache |
| behavior. |
| |
| Reported-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Dan Williams <dan.j.williams@intel.com> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Cc: linux-arch@vger.kernel.org |
| Cc: kernel-hardening@lists.openwall.com |
| Cc: gregkh@linuxfoundation.org |
| Cc: Andy Lutomirski <luto@kernel.org> |
| Cc: alan@linux.intel.com |
| Link: https://lkml.kernel.org/r/151727417984.33451.1216731042505722161.stgit@dwillia2-desk3.amr.corp.intel.com |
| Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| arch/x86/entry/common.c | 5 ++++- |
| 1 file changed, 4 insertions(+), 1 deletion(-) |
| |
| --- a/arch/x86/entry/common.c |
| +++ b/arch/x86/entry/common.c |
| @@ -20,6 +20,7 @@ |
| #include <linux/export.h> |
| #include <linux/context_tracking.h> |
| #include <linux/user-return-notifier.h> |
| +#include <linux/nospec.h> |
| #include <linux/uprobes.h> |
| |
| #include <asm/desc.h> |
| @@ -277,7 +278,8 @@ __visible void do_syscall_64(struct pt_r |
| * regs->orig_ax, which changes the behavior of some syscalls. |
| */ |
| if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { |
| - regs->ax = sys_call_table[nr & __SYSCALL_MASK]( |
| + nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls); |
| + regs->ax = sys_call_table[nr]( |
| regs->di, regs->si, regs->dx, |
| regs->r10, regs->r8, regs->r9); |
| } |
| @@ -313,6 +315,7 @@ static __always_inline void do_syscall_3 |
| } |
| |
| if (likely(nr < IA32_NR_syscalls)) { |
| + nr = array_index_nospec(nr, IA32_NR_syscalls); |
| /* |
| * It's possible that a 32-bit syscall implementation |
| * takes a 64-bit parameter but nonetheless assumes that |
