From: Kyle Huey <[email protected]>
When management of the PKRU register was moved away from XSTATE, emulation
of PKRU's existence in XSTATE was added for reading PKRU through ptrace,
but not for writing PKRU through ptrace. 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 APIs that write PKRU: sigreturn, PTRACE_SETREGSET with
NT_X86_XSTATE, and KVM_SET_XSAVE. sigreturn still uses XRSTOR to write to
PKRU. 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 pass in
a pointer to the appropriate PKRU slot. copy_sigframe_from_user_to_xstate
depends on copy_uabi_to_xstate populating the PKRU field in the task's
XSTATE so that __fpu_restore_sig can do a XRSTOR from it, so continue doing
that.
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 provided to
ptrace, to match XRSTOR.
Fixes: e84ba47e313d ("x86/fpu: Hook up PKRU into ptrace()")
Signed-off-by: Kyle Huey <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: [email protected] # 5.14+
---
arch/x86/kernel/fpu/core.c | 20 +++++++++-----------
arch/x86/kernel/fpu/regset.c | 2 +-
arch/x86/kernel/fpu/signal.c | 2 +-
arch/x86/kernel/fpu/xstate.c | 25 ++++++++++++++++++++-----
arch/x86/kernel/fpu/xstate.h | 4 ++--
5 files changed, 33 insertions(+), 20 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 3b28c5b25e12..c273669e8a00 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -391,8 +391,6 @@ int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
{
struct fpstate *kstate = gfpu->fpstate;
const union fpregs_state *ustate = buf;
- struct pkru_state *xpkru;
- int ret;
if (!cpu_feature_enabled(X86_FEATURE_XSAVE)) {
if (ustate->xsave.header.xfeatures & ~XFEATURE_MASK_FPSSE)
@@ -406,16 +404,16 @@ int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
if (ustate->xsave.header.xfeatures & ~xcr0)
return -EINVAL;
- ret = copy_uabi_from_kernel_to_xstate(kstate, ustate);
- if (ret)
- return ret;
+ /*
+ * Nullify @vpkru to preserve its current value if PKRU's bit isn't set
+ * in the header. KVM's odd ABI is to leave PKRU untouched in this
+ * case (all other components are eventually re-initialized).
+ * (Not clear that this is actually necessary for compat).
+ */
+ if (!(ustate->xsave.header.xfeatures & XFEATURE_MASK_PKRU))
+ vpkru = NULL;
- /* Retrieve PKRU if not in init state */
- if (kstate->regs.xsave.header.xfeatures & XFEATURE_MASK_PKRU) {
- xpkru = get_xsave_addr(&kstate->regs.xsave, XFEATURE_PKRU);
- *vpkru = xpkru->pkru;
- }
- return 0;
+ return copy_uabi_from_kernel_to_xstate(kstate, ustate, vpkru);
}
EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate);
#endif /* CONFIG_KVM */
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 75ffaef8c299..6d056b68f4ed 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -167,7 +167,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
}
fpu_force_restore(fpu);
- ret = copy_uabi_from_kernel_to_xstate(fpu->fpstate, kbuf ?: tmpbuf);
+ ret = copy_uabi_from_kernel_to_xstate(fpu->fpstate, kbuf ?: tmpbuf, &target->thread.pkru);
out:
vfree(tmpbuf);
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 91d4b6de58ab..558076dbde5b 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -396,7 +396,7 @@ static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
fpregs = &fpu->fpstate->regs;
if (use_xsave() && !fx_only) {
- if (copy_sigframe_from_user_to_xstate(fpu->fpstate, buf_fx))
+ if (copy_sigframe_from_user_to_xstate(tsk, buf_fx))
return false;
} else {
if (__copy_from_user(&fpregs->fxsave, buf_fx,
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index c8340156bfd2..8f14981a3936 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1197,7 +1197,7 @@ static int copy_from_buffer(void *dst, unsigned int offset, unsigned int size,
static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
- const void __user *ubuf)
+ const void __user *ubuf, u32 *pkru)
{
struct xregs_state *xsave = &fpstate->regs.xsave;
unsigned int offset, size;
@@ -1246,6 +1246,21 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
}
}
+ /*
+ * Update the user protection key storage. Allow KVM to
+ * pass in a NULL pkru pointer if the mask bit is unset
+ * for its legacy ABI behavior.
+ */
+ if (pkru)
+ *pkru = 0;
+
+ if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
+ struct pkru_state *xpkru;
+
+ xpkru = __raw_xsave_addr(xsave, XFEATURE_PKRU);
+ *pkru = xpkru->pkru;
+ }
+
/*
* The state that came in from userspace was user-state only.
* Mask all the user states out of 'xfeatures':
@@ -1264,9 +1279,9 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
* Convert from a ptrace standard-format kernel buffer to kernel XSAVE[S]
* format and copy to the target thread. Used by ptrace and KVM.
*/
-int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf)
+int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru)
{
- return copy_uabi_to_xstate(fpstate, kbuf, NULL);
+ return copy_uabi_to_xstate(fpstate, kbuf, NULL, pkru);
}
/*
@@ -1274,10 +1289,10 @@ int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf)
* XSAVE[S] format and copy to the target thread. This is called from the
* sigreturn() and rt_sigreturn() system calls.
*/
-int copy_sigframe_from_user_to_xstate(struct fpstate *fpstate,
+int copy_sigframe_from_user_to_xstate(struct task_struct *tsk,
const void __user *ubuf)
{
- return copy_uabi_to_xstate(fpstate, NULL, ubuf);
+ return copy_uabi_to_xstate(tsk->thread.fpu.fpstate, NULL, ubuf, &tsk->thread.pkru);
}
static bool validate_independent_components(u64 mask)
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 5ad47031383b..a4ecb04d8d64 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -46,8 +46,8 @@ extern void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
u32 pkru_val, enum xstate_copy_mode copy_mode);
extern void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
enum xstate_copy_mode mode);
-extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf);
-extern int copy_sigframe_from_user_to_xstate(struct fpstate *fpstate, const void __user *ubuf);
+extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru);
+extern int copy_sigframe_from_user_to_xstate(struct task_struct *tsk, const void __user *ubuf);
extern void fpu__init_cpu_xstate(void);
--
2.37.2
Changelog since v5:
- Avoids a second copy from the uabi buffer as suggested.
- Preserves old KVM_SET_XSAVE behavior where leaving the PKRU bit in the
XSTATE header results in PKRU remaining unchanged instead of
reinitializing it.
- Fixed up patch metadata as requested.
Changelog since v4:
- Selftest additionally checks PKRU readbacks through ptrace.
- Selftest flips all PKRU bits (except the default key).
Changelog since v3:
- The v3 patch is now part 1 of 2.
- Adds a selftest in part 2 of 2.
Changelog since v2:
- Removed now unused variables in fpu_copy_uabi_to_guest_fpstate
Changelog since v1:
- Handles the error case of copy_to_buffer().
From: Kyle Huey <[email protected]>
This tests PTRACE_SETREGSET with NT_X86_XSTATE modifying PKRU directly and
removing the PKRU bit from XSTATE_BV.
Signed-off-by: Kyle Huey <[email protected]>
---
tools/testing/selftests/vm/pkey-x86.h | 12 ++
tools/testing/selftests/vm/protection_keys.c | 131 ++++++++++++++++++-
2 files changed, 141 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/vm/pkey-x86.h b/tools/testing/selftests/vm/pkey-x86.h
index b078ce9c6d2a..72c14cd3ddc7 100644
--- a/tools/testing/selftests/vm/pkey-x86.h
+++ b/tools/testing/selftests/vm/pkey-x86.h
@@ -104,6 +104,18 @@ static inline int cpu_has_pkeys(void)
return 1;
}
+static inline int cpu_max_xsave_size(void)
+{
+ unsigned long XSTATE_CPUID = 0xd;
+ unsigned int eax;
+ unsigned int ebx;
+ unsigned int ecx;
+ unsigned int edx;
+
+ __cpuid_count(XSTATE_CPUID, 0, eax, ebx, ecx, edx);
+ return ecx;
+}
+
static inline u32 pkey_bit_position(int pkey)
{
return pkey * PKEY_BITS_PER_PKEY;
diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c
index 291bc1e07842..95f403a0c46d 100644
--- a/tools/testing/selftests/vm/protection_keys.c
+++ b/tools/testing/selftests/vm/protection_keys.c
@@ -18,12 +18,13 @@
* do a plain mprotect() to a mprotect_pkey() area and make sure the pkey sticks
*
* Compile like this:
- * gcc -o protection_keys -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
- * gcc -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
+ * gcc -mxsave -o protection_keys -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
+ * gcc -mxsave -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
*/
#define _GNU_SOURCE
#define __SANE_USERSPACE_TYPES__
#include <errno.h>
+#include <linux/elf.h>
#include <linux/futex.h>
#include <time.h>
#include <sys/time.h>
@@ -1550,6 +1551,129 @@ void test_implicit_mprotect_exec_only_memory(int *ptr, u16 pkey)
do_not_expect_pkey_fault("plain read on recently PROT_EXEC area");
}
+#if defined(__i386__) || defined(__x86_64__)
+void test_ptrace_modifies_pkru(int *ptr, u16 pkey)
+{
+ u32 new_pkru;
+ pid_t child;
+ int status, ret;
+ int pkey_offset = pkey_reg_xstate_offset();
+ size_t xsave_size = cpu_max_xsave_size();
+ void *xsave;
+ u32 *pkey_register;
+ u64 *xstate_bv;
+ struct iovec iov;
+
+ new_pkru = ~read_pkey_reg();
+ /* Don't make PROT_EXEC mappings inaccessible */
+ new_pkru &= ~3;
+
+ child = fork();
+ pkey_assert(child >= 0);
+ dprintf3("[%d] fork() ret: %d\n", getpid(), child);
+ if (!child) {
+ ptrace(PTRACE_TRACEME, 0, 0, 0);
+ /* Stop and allow the tracer to modify PKRU directly */
+ raise(SIGSTOP);
+
+ /*
+ * need __read_pkey_reg() version so we do not do shadow_pkey_reg
+ * checking
+ */
+ if (__read_pkey_reg() != new_pkru)
+ exit(1);
+
+ /* Stop and allow the tracer to clear XSTATE_BV for PKRU */
+ raise(SIGSTOP);
+
+ if (__read_pkey_reg() != 0)
+ exit(1);
+
+ /* Stop and allow the tracer to examine PKRU */
+ raise(SIGSTOP);
+
+ exit(0);
+ }
+
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+
+ xsave = (void *)malloc(xsave_size);
+ pkey_assert(xsave > 0);
+
+ /* Modify the PKRU register directly */
+ iov.iov_base = xsave;
+ iov.iov_len = xsave_size;
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ pkey_register = (u32 *)(xsave + pkey_offset);
+ pkey_assert(*pkey_register == read_pkey_reg());
+
+ *pkey_register = new_pkru;
+
+ ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ /* Test that the modification is visible in ptrace before any execution */
+ memset(xsave, 0xCC, xsave_size);
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+ pkey_assert(*pkey_register == new_pkru);
+
+ /* Execute the tracee */
+ ret = ptrace(PTRACE_CONT, child, 0, 0);
+ pkey_assert(ret == 0);
+
+ /* Test that the tracee saw the PKRU value change */
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+
+ /* Test that the modification is visible in ptrace after execution */
+ memset(xsave, 0xCC, xsave_size);
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+ pkey_assert(*pkey_register == new_pkru);
+
+ /* Clear the PKRU bit from XSTATE_BV */
+ xstate_bv = (u64 *)(xsave + 512);
+ *xstate_bv &= ~(1 << 9);
+
+ ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ /* Test that the modification is visible in ptrace before any execution */
+ memset(xsave, 0xCC, xsave_size);
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+ pkey_assert(*pkey_register == 0);
+
+ ret = ptrace(PTRACE_CONT, child, 0, 0);
+ pkey_assert(ret == 0);
+
+ /* Test that the tracee saw the PKRU value go to 0 */
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+
+ /* Test that the modification is visible in ptrace after execution */
+ memset(xsave, 0xCC, xsave_size);
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+ pkey_assert(*pkey_register == 0);
+
+ ret = ptrace(PTRACE_CONT, child, 0, 0);
+ pkey_assert(ret == 0);
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFEXITED(status));
+ pkey_assert(WEXITSTATUS(status) == 0);
+ free(xsave);
+}
+#endif
+
void test_mprotect_pkey_on_unsupported_cpu(int *ptr, u16 pkey)
{
int size = PAGE_SIZE;
@@ -1585,6 +1709,9 @@ void (*pkey_tests[])(int *ptr, u16 pkey) = {
test_pkey_syscalls_bad_args,
test_pkey_alloc_exhaust,
test_pkey_alloc_free_attach_pkey0,
+#if defined(__i386__) || defined(__x86_64__)
+ test_ptrace_modifies_pkru,
+#endif
};
void run_tests_once(void)
--
2.37.2
On Mon, Aug 29, 2022, Kyle Huey wrote:
> @@ -1246,6 +1246,21 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
> }
> }
>
> + /*
> + * Update the user protection key storage. Allow KVM to
> + * pass in a NULL pkru pointer if the mask bit is unset
> + * for its legacy ABI behavior.
> + */
> + if (pkru)
> + *pkru = 0;
> +
> + if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
> + struct pkru_state *xpkru;
> +
> + xpkru = __raw_xsave_addr(xsave, XFEATURE_PKRU);
> + *pkru = xpkru->pkru;
> + }
What about writing this as:
if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
...
*pkru = xpkru->pkru;
} else if (pkru) {
*pkru = 0;
}
to make it slightly more obvious that @pkru must be non-NULL if the feature flag
is enabled?
Or we could be paranoid, though I'm not sure this is worthwhile.
if ((hdr.xfeatures & XFEATURE_MASK_PKRU) &&
!WARN_ON_ONCE(!pkru)) {
...
*pkru = xpkru->pkru;
} else if (pkru) {
*pkru = 0;
}
Otherwise, looks good from a KVM perspective. Thanks!
On Thu, Sep 1, 2022 at 8:29 AM Sean Christopherson <[email protected]> wrote:
>
> On Mon, Aug 29, 2022, Kyle Huey wrote:
> > @@ -1246,6 +1246,21 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
> > }
> > }
> >
> > + /*
> > + * Update the user protection key storage. Allow KVM to
> > + * pass in a NULL pkru pointer if the mask bit is unset
> > + * for its legacy ABI behavior.
> > + */
> > + if (pkru)
> > + *pkru = 0;
> > +
> > + if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
> > + struct pkru_state *xpkru;
> > +
> > + xpkru = __raw_xsave_addr(xsave, XFEATURE_PKRU);
> > + *pkru = xpkru->pkru;
> > + }
>
> What about writing this as:
>
> if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
> ...
>
> *pkru = xpkru->pkru;
> } else if (pkru) {
> *pkru = 0;
> }
>
> to make it slightly more obvious that @pkru must be non-NULL if the feature flag
> is enabled?
tglx didn't seem to like the branchiness before but maybe he'll change
his mind since we have to have the `if (pkru)` now anyways.
> Or we could be paranoid, though I'm not sure this is worthwhile.
>
> if ((hdr.xfeatures & XFEATURE_MASK_PKRU) &&
> !WARN_ON_ONCE(!pkru)) {
> ...
>
> *pkru = xpkru->pkru;
> } else if (pkru) {
> *pkru = 0;
> }
I don't feel strongly about this.
> Otherwise, looks good from a KVM perspective. Thanks!
Great.
- Kyle
On Mon, Aug 29, 2022 at 12:49 PM Kyle Huey <[email protected]> wrote:
>
> From: Kyle Huey <[email protected]>
>
> When management of the PKRU register was moved away from XSTATE, emulation
> of PKRU's existence in XSTATE was added for reading PKRU through ptrace,
> but not for writing PKRU through ptrace. 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 APIs that write PKRU: sigreturn, PTRACE_SETREGSET with
> NT_X86_XSTATE, and KVM_SET_XSAVE. sigreturn still uses XRSTOR to write to
> PKRU. 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 pass in
> a pointer to the appropriate PKRU slot. copy_sigframe_from_user_to_xstate
> depends on copy_uabi_to_xstate populating the PKRU field in the task's
> XSTATE so that __fpu_restore_sig can do a XRSTOR from it, so continue doing
> that.
>
> 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 provided to
> ptrace, to match XRSTOR.
>
> Fixes: e84ba47e313d ("x86/fpu: Hook up PKRU into ptrace()")
> Signed-off-by: Kyle Huey <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: [email protected] # 5.14+
> ---
> arch/x86/kernel/fpu/core.c | 20 +++++++++-----------
> arch/x86/kernel/fpu/regset.c | 2 +-
> arch/x86/kernel/fpu/signal.c | 2 +-
> arch/x86/kernel/fpu/xstate.c | 25 ++++++++++++++++++++-----
> arch/x86/kernel/fpu/xstate.h | 4 ++--
> 5 files changed, 33 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 3b28c5b25e12..c273669e8a00 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -391,8 +391,6 @@ int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
> {
> struct fpstate *kstate = gfpu->fpstate;
> const union fpregs_state *ustate = buf;
> - struct pkru_state *xpkru;
> - int ret;
>
> if (!cpu_feature_enabled(X86_FEATURE_XSAVE)) {
> if (ustate->xsave.header.xfeatures & ~XFEATURE_MASK_FPSSE)
> @@ -406,16 +404,16 @@ int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
> if (ustate->xsave.header.xfeatures & ~xcr0)
> return -EINVAL;
>
> - ret = copy_uabi_from_kernel_to_xstate(kstate, ustate);
> - if (ret)
> - return ret;
> + /*
> + * Nullify @vpkru to preserve its current value if PKRU's bit isn't set
> + * in the header. KVM's odd ABI is to leave PKRU untouched in this
> + * case (all other components are eventually re-initialized).
> + * (Not clear that this is actually necessary for compat).
> + */
> + if (!(ustate->xsave.header.xfeatures & XFEATURE_MASK_PKRU))
> + vpkru = NULL;
>
> - /* Retrieve PKRU if not in init state */
> - if (kstate->regs.xsave.header.xfeatures & XFEATURE_MASK_PKRU) {
> - xpkru = get_xsave_addr(&kstate->regs.xsave, XFEATURE_PKRU);
> - *vpkru = xpkru->pkru;
> - }
> - return 0;
> + return copy_uabi_from_kernel_to_xstate(kstate, ustate, vpkru);
> }
> EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate);
> #endif /* CONFIG_KVM */
> diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
> index 75ffaef8c299..6d056b68f4ed 100644
> --- a/arch/x86/kernel/fpu/regset.c
> +++ b/arch/x86/kernel/fpu/regset.c
> @@ -167,7 +167,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
> }
>
> fpu_force_restore(fpu);
> - ret = copy_uabi_from_kernel_to_xstate(fpu->fpstate, kbuf ?: tmpbuf);
> + ret = copy_uabi_from_kernel_to_xstate(fpu->fpstate, kbuf ?: tmpbuf, &target->thread.pkru);
>
> out:
> vfree(tmpbuf);
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index 91d4b6de58ab..558076dbde5b 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -396,7 +396,7 @@ static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
>
> fpregs = &fpu->fpstate->regs;
> if (use_xsave() && !fx_only) {
> - if (copy_sigframe_from_user_to_xstate(fpu->fpstate, buf_fx))
> + if (copy_sigframe_from_user_to_xstate(tsk, buf_fx))
> return false;
> } else {
> if (__copy_from_user(&fpregs->fxsave, buf_fx,
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index c8340156bfd2..8f14981a3936 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -1197,7 +1197,7 @@ static int copy_from_buffer(void *dst, unsigned int offset, unsigned int size,
>
>
> static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
> - const void __user *ubuf)
> + const void __user *ubuf, u32 *pkru)
> {
> struct xregs_state *xsave = &fpstate->regs.xsave;
> unsigned int offset, size;
> @@ -1246,6 +1246,21 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
> }
> }
>
> + /*
> + * Update the user protection key storage. Allow KVM to
> + * pass in a NULL pkru pointer if the mask bit is unset
> + * for its legacy ABI behavior.
> + */
> + if (pkru)
> + *pkru = 0;
> +
> + if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
> + struct pkru_state *xpkru;
> +
> + xpkru = __raw_xsave_addr(xsave, XFEATURE_PKRU);
> + *pkru = xpkru->pkru;
> + }
> +
> /*
> * The state that came in from userspace was user-state only.
> * Mask all the user states out of 'xfeatures':
> @@ -1264,9 +1279,9 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
> * Convert from a ptrace standard-format kernel buffer to kernel XSAVE[S]
> * format and copy to the target thread. Used by ptrace and KVM.
> */
> -int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf)
> +int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru)
> {
> - return copy_uabi_to_xstate(fpstate, kbuf, NULL);
> + return copy_uabi_to_xstate(fpstate, kbuf, NULL, pkru);
> }
>
> /*
> @@ -1274,10 +1289,10 @@ int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf)
> * XSAVE[S] format and copy to the target thread. This is called from the
> * sigreturn() and rt_sigreturn() system calls.
> */
> -int copy_sigframe_from_user_to_xstate(struct fpstate *fpstate,
> +int copy_sigframe_from_user_to_xstate(struct task_struct *tsk,
> const void __user *ubuf)
> {
> - return copy_uabi_to_xstate(fpstate, NULL, ubuf);
> + return copy_uabi_to_xstate(tsk->thread.fpu.fpstate, NULL, ubuf, &tsk->thread.pkru);
> }
>
> static bool validate_independent_components(u64 mask)
> diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
> index 5ad47031383b..a4ecb04d8d64 100644
> --- a/arch/x86/kernel/fpu/xstate.h
> +++ b/arch/x86/kernel/fpu/xstate.h
> @@ -46,8 +46,8 @@ extern void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
> u32 pkru_val, enum xstate_copy_mode copy_mode);
> extern void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
> enum xstate_copy_mode mode);
> -extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf);
> -extern int copy_sigframe_from_user_to_xstate(struct fpstate *fpstate, const void __user *ubuf);
> +extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru);
> +extern int copy_sigframe_from_user_to_xstate(struct task_struct *tsk, const void __user *ubuf);
>
>
> extern void fpu__init_cpu_xstate(void);
> --
> 2.37.2
>
> Changelog since v5:
> - Avoids a second copy from the uabi buffer as suggested.
> - Preserves old KVM_SET_XSAVE behavior where leaving the PKRU bit in the
> XSTATE header results in PKRU remaining unchanged instead of
> reinitializing it.
> - Fixed up patch metadata as requested.
>
> Changelog since v4:
> - Selftest additionally checks PKRU readbacks through ptrace.
> - Selftest flips all PKRU bits (except the default key).
>
> Changelog since v3:
> - The v3 patch is now part 1 of 2.
> - Adds a selftest in part 2 of 2.
>
> Changelog since v2:
> - Removed now unused variables in fpu_copy_uabi_to_guest_fpstate
>
> Changelog since v1:
> - Handles the error case of copy_to_buffer().
tglx, could you look at this again?
- Kyle