diff options
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 7 | ||||
| -rw-r--r-- | arch/x86/Kconfig | 33 | ||||
| -rw-r--r-- | arch/x86/entry/vsyscall/vsyscall_64.c | 16 |
3 files changed, 44 insertions, 12 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 0082d1e56999..be8c3a680afa 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5100,7 +5100,12 @@ targets for exploits that can control RIP. emulate [default] Vsyscalls turn into traps and are - emulated reasonably safely. + emulated reasonably safely. The vsyscall + page is readable. + + xonly Vsyscalls turn into traps and are + emulated reasonably safely. The vsyscall + page is not readable. none Vsyscalls don't work at all. This makes them quite hard to use for exploits but diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 2bbbd4d1ba31..0182d2c67590 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2293,23 +2293,38 @@ choice it can be used to assist security vulnerability exploitation. This setting can be changed at boot time via the kernel command - line parameter vsyscall=[emulate|none]. + line parameter vsyscall=[emulate|xonly|none]. On a system with recent enough glibc (2.14 or newer) and no static binaries, you can say None without a performance penalty to improve security. - If unsure, select "Emulate". + If unsure, select "Emulate execution only". config LEGACY_VSYSCALL_EMULATE - bool "Emulate" + bool "Full emulation" help - The kernel traps and emulates calls into the fixed - vsyscall address mapping. This makes the mapping - non-executable, but it still contains known contents, - which could be used in certain rare security vulnerability - exploits. This configuration is recommended when userspace - still uses the vsyscall area. + The kernel traps and emulates calls into the fixed vsyscall + address mapping. This makes the mapping non-executable, but + it still contains readable known contents, which could be + used in certain rare security vulnerability exploits. This + configuration is recommended when using legacy userspace + that still uses vsyscalls along with legacy binary + instrumentation tools that require code to be readable. + + An example of this type of legacy userspace is running + Pin on an old binary that still uses vsyscalls. + + config LEGACY_VSYSCALL_XONLY + bool "Emulate execution only" + help + The kernel traps and emulates calls into the fixed vsyscall + address mapping and does not allow reads. This + configuration is recommended when userspace might use the + legacy vsyscall area but support for legacy binary + instrumentation of legacy code is not needed. It mitigates + certain uses of the vsyscall area as an ASLR-bypassing + buffer. config LEGACY_VSYSCALL_NONE bool "None" diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index d9d81ad7a400..fedd7628f3a6 100644 --- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -42,9 +42,11 @@ #define CREATE_TRACE_POINTS #include "vsyscall_trace.h" -static enum { EMULATE, NONE } vsyscall_mode = +static enum { EMULATE, XONLY, NONE } vsyscall_mode = #ifdef CONFIG_LEGACY_VSYSCALL_NONE NONE; +#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY) + XONLY; #else EMULATE; #endif @@ -54,6 +56,8 @@ static int __init vsyscall_setup(char *str) if (str) { if (!strcmp("emulate", str)) vsyscall_mode = EMULATE; + else if (!strcmp("xonly", str)) + vsyscall_mode = XONLY; else if (!strcmp("none", str)) vsyscall_mode = NONE; else @@ -357,12 +361,20 @@ void __init map_vsyscall(void) extern char __vsyscall_page; unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page); - if (vsyscall_mode != NONE) { + /* + * For full emulation, the page needs to exist for real. In + * execute-only mode, there is no PTE at all backing the vsyscall + * page. + */ + if (vsyscall_mode == EMULATE) { __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall, PAGE_KERNEL_VVAR); set_vsyscall_pgtable_user_bits(swapper_pg_dir); } + if (vsyscall_mode == XONLY) + gate_vma.vm_flags = VM_EXEC; + BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != (unsigned long)VSYSCALL_ADDR); } |