Changes since v2 [1]: * Interleave clearing with preserving in the syscall and compat syscall path (Linus)
* Extend clearing protection to r10 and r11 in the sycall path and r8 + r9 in the compat syscall path. (Ingo) * Drop some redundant clearing at interrupt / exception entry. [1]: https://lkml.org/lkml/2018/2/4/125 --- At entry userspace may have populated callee saved registers with values that could be useful in a speculative execution attack. Clear them to minimize the kernel's attack surface. Note, this is done to make it harder to find / manipulate exploitable sequences in the kernel. The clearing is limited to the 64-bit 'extra' registers since those are the most likely to survive with user populated values deep into the call chain. Normal register pressure likely clobbers values in the lower registers and the 32-bit case. As for cycle impact, interleaving the clearing with pushing values onto the stack hides most the overhead. --- Andi Kleen (2): x86/entry: Clear registers for 64bit exceptions/interrupts x86/entry: Clear registers for compat syscalls Dan Williams (1): x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels arch/x86/entry/calling.h | 19 +++++++++++++++++++ arch/x86/entry/entry_64.S | 20 ++++++++++++++++++-- arch/x86/entry/entry_64_compat.S | 30 ++++++++++++++++++++++++++++++ 3 files changed, 67 insertions(+), 2 deletions(-)
