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Date: Thu, 18 Aug 2022 12:57:04 +0200 From: Thomas Gleixner <tglx@...utronix.de> To: Kyle Huey <me@...ehuey.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Borislav Petkov <bp@...en8.de> Cc: Ingo Molnar <mingo@...hat.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, Robert O'Callahan <robert@...llahan.org>, David Manouchehri <david.manouchehri@...eup.net>, Kyle Huey <me@...ehuey.com>, Borislav Petkov <bp@...e.de>, kvm@...r.kernel.org, stable@...r.kernel.org Subject: Re: [PATCH v5 1/2] x86/fpu: Allow PKRU to be (once again) written by ptrace. Kyle! On Mon, Aug 08 2022 at 07:15, Kyle Huey wrote: > When management of the PKRU register was moved away from XSTATE, emulation > of PKRU's existence in XSTATE was added for APIs that read XSTATE, but not > for APIs that write XSTATE. This can be seen by running gdb and executing > `p $pkru`, `set $pkru = 42`, and `p $pkru`. On affected kernels (5.14+) the > write to the PKRU register (which gdb performs through ptrace) is ignored. > > There are three relevant APIs: PTRACE_SETREGSET with NT_X86_XSTATE, > sigreturn, and KVM_SET_XSAVE. KVM_SET_XSAVE has its own special handling to > make PKRU writes take effect (in fpu_copy_uabi_to_guest_fpstate). Push that > down into copy_uabi_to_xstate and have PTRACE_SETREGSET with NT_X86_XSTATE > and sigreturn pass in pointers to the appropriate PKRU value. > > This also adds code to initialize the PKRU value to the hardware init value > (namely 0) if the PKRU bit is not set in the XSTATE header to match XRSTOR. > This is a change to the current KVM_SET_XSAVE behavior. You are stating a fact here, but provide 0 justification why this is correct. > > Changelog since v4: Can you please put the change log past the --- seperator line, so it gets stripped off when the patch is applied? That spares manual fixups. > > Signed-off-by: Kyle Huey <me@...ehuey.com> > Cc: Dave Hansen <dave.hansen@...ux.intel.com> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Borislav Petkov <bp@...e.de> > Cc: kvm@...r.kernel.org # For edge case behavior of KVM_SET_XSAVE > Cc: stable@...r.kernel.org # 5.14+ > Fixes: e84ba47e313d ("x86/fpu: Hook up PKRU into ptrace()") Can you please use the documented tag ordering? https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#patch-submission-notes > @@ -1235,6 +1235,24 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf, > for (i = 0; i < XFEATURE_MAX; i++) { > mask = BIT_ULL(i); > > + if (i == XFEATURE_PKRU) { > + /* > + * Retrieve PKRU if not in init state, otherwise > + * initialize it. > + */ > + if (hdr.xfeatures & mask) { > + struct pkru_state xpkru = {0}; > + > + if (copy_from_buffer(&xpkru, xstate_offsets[i], > + sizeof(xpkru), kbuf, ubuf)) > + return -EFAULT; > + > + *pkru = xpkru.pkru; > + } else { > + *pkru = 0; > + } > + } That's really horrible and there is no point in copying the stuff from the buffer twice: @@ -1246,6 +1246,15 @@ static int copy_uabi_to_xstate(struct fp } } + /* Update the user protection key storage */ + *pkru = 0; + if (hdr.xfeatures & XFEATURE_MASK_PKRU) { + struct pkru_state *xpkru; + + xpkru = get_xsave_addr(xsave, XFEATURE_PKRU); + *pkru = xpkru->pkru; + } + Hmm? Thanks, tglx
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