ptrace() may update xstate data before the target task has taken an XFD fault and expanded the context switch buffer. Detect this case and allocate a sufficient buffer to support the request. Also, disable the (now unnecessary) associated first-use fault.
No functional change until the kernel supports dynamic user states. Signed-off-by: Chang S. Bae <[email protected]> Reviewed-by: Len Brown <[email protected]> Cc: [email protected] Cc: [email protected] --- Changes from v2: * Updated the changelog with task->fpu removed. (Boris Petkov) * Updated the code comments. --- arch/x86/kernel/fpu/regset.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c index 8d863240b9c6..16ff8ac765c1 100644 --- a/arch/x86/kernel/fpu/regset.c +++ b/arch/x86/kernel/fpu/regset.c @@ -125,6 +125,35 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset, xsave = __xsave(fpu); + /* + * When a ptracer attempts to write any state in the target buffer but not + * sufficiently allocated, it dynamically expands the buffer. + */ + if (count > get_xstate_size(fpu->state_mask)) { + unsigned int offset, size; + struct xstate_header hdr; + u64 mask; + + offset = offsetof(struct xregs_state, header); + size = sizeof(hdr); + + /* Retrieve XSTATE_BV */ + if (kbuf) { + memcpy(&hdr, kbuf + offset, size); + } else { + ret = __copy_from_user(&hdr, ubuf + offset, size); + if (ret) + return ret; + } + + mask = hdr.xfeatures & xfeatures_mask_user_dynamic; + if (!mask) { + ret = alloc_xstate_buffer(fpu, mask); + if (ret) + return ret; + } + } + fpu__prepare_write(fpu); if (using_compacted_format()) { -- 2.17.1
