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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2021-04-26 10:02:09 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-04-26 10:02:09 -0700 |
| commit | eea2647e74cd7bd5d04861ce55fa502de165de14 (patch) | |
| tree | 6d8fc43f3b8762651f825e74fc20f79d20f054a9 /arch/x86/entry | |
| parent | 6f78c2a7b7219bc2e455250365f438621e5819d0 (diff) | |
| parent | 70918779aec9bd01d16f4e6e800ffe423d196021 (diff) | |
Merge tag 'x86-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull entry code update from Thomas Gleixner:
"Provide support for randomized stack offsets per syscall to make
stack-based attacks harder which rely on the deterministic stack
layout.
The feature is based on the original idea of PaX's RANDSTACK feature,
but uses a significantly different implementation.
The offset does not affect the pt_regs location on the task stack as
this was agreed on to be of dubious value. The offset is applied
before the actual syscall is invoked.
The offset is stored per cpu and the randomization happens at the end
of the syscall which is less predictable than on syscall entry.
The mechanism to apply the offset is via alloca(), i.e. abusing the
dispised VLAs. This comes with the drawback that
stack-clash-protection has to be disabled for the affected compilation
units and there is also a negative interaction with stack-protector.
Those downsides are traded with the advantage that this approach does
not require any intrusive changes to the low level assembly entry
code, does not affect the unwinder and the correct stack alignment is
handled automatically by the compiler.
The feature is guarded with a static branch which avoids the overhead
when disabled.
Currently this is supported for X86 and ARM64"
* tag 'x86-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
arm64: entry: Enable random_kstack_offset support
lkdtm: Add REPORT_STACK for checking stack offsets
x86/entry: Enable random_kstack_offset support
stack: Optionally randomize kernel stack offset each syscall
init_on_alloc: Optimize static branches
jump_label: Provide CONFIG-driven build state defaults
Diffstat (limited to 'arch/x86/entry')
| -rw-r--r-- | arch/x86/entry/common.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 4efd39aacb9f..7b2542b13ebd 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -38,6 +38,7 @@ #ifdef CONFIG_X86_64 __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs) { + add_random_kstack_offset(); nr = syscall_enter_from_user_mode(regs, nr); instrumentation_begin(); @@ -83,6 +84,7 @@ __visible noinstr void do_int80_syscall_32(struct pt_regs *regs) { unsigned int nr = syscall_32_enter(regs); + add_random_kstack_offset(); /* * Subtlety here: if ptrace pokes something larger than 2^32-1 into * orig_ax, the unsigned int return value truncates it. This may @@ -102,6 +104,7 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs) unsigned int nr = syscall_32_enter(regs); int res; + add_random_kstack_offset(); /* * This cannot use syscall_enter_from_user_mode() as it has to * fetch EBP before invoking any of the syscall entry work |