x86/mm/pkeys: Fix compact mode by removing protection keys' XSAVE buffer manipulation (b79daf85) · Commits · 戴 / test

arch/x86/kernel/fpu/xstate.c

+17 −121

Original line number	Diff line number	Diff line
		@@ -866,105 +866,17 @@ const void *get_xsave_field_ptr(int xsave_state)
		return get_xsave_addr(&fpu->state.xsave, xsave_state);
		}


		/*
		* Set xfeatures (aka XSTATE_BV) bit for a feature that we want
		* to take out of its "init state". This will ensure that an
		* XRSTOR actually restores the state.
		*/
		static void fpu__xfeature_set_non_init(struct xregs_state *xsave,
		int xstate_feature_mask)
		{
		xsave->header.xfeatures \|= xstate_feature_mask;
		}

		/*
		* This function is safe to call whether the FPU is in use or not.
		*
		* Note that this only works on the current task.
		*
		* Inputs:
		* @xsave_state: state which is defined in xsave.h (e.g. XFEATURE_MASK_FP,
		* XFEATURE_MASK_SSE, etc...)
		* @xsave_state_ptr: a pointer to a copy of the state that you would
		* like written in to the current task's FPU xsave state. This pointer
		* must not be located in the current tasks's xsave area.
		* Output:
		* address of the state in the xsave area or NULL if the state
		* is not present or is in its 'init state'.
		*/
		static void fpu__xfeature_set_state(int xstate_feature_mask,
		void *xstate_feature_src, size_t len)
		{
		struct xregs_state *xsave = &current->thread.fpu.state.xsave;
		struct fpu *fpu = &current->thread.fpu;
		void *dst;

		if (!boot_cpu_has(X86_FEATURE_XSAVE)) {
		WARN_ONCE(1, "%s() attempted with no xsave support", __func__);
		return;
		}

		/*
		* Tell the FPU code that we need the FPU state to be in
		* 'fpu' (not in the registers), and that we need it to
		* be stable while we write to it.
		*/
		fpu__current_fpstate_write_begin();

		/*
		* This method WILL NOT work for compact-format
		* buffers. If the 'xstate_feature_mask' is unset in
		* xcomp_bv then we may need to move other feature state
		* "up" in the buffer.
		*/
		if (xsave->header.xcomp_bv & xstate_feature_mask) {
		WARN_ON_ONCE(1);
		goto out;
		}

		/* find the location in the xsave buffer of the desired state */
		dst = __raw_xsave_addr(&fpu->state.xsave, xstate_feature_mask);

		/*
		* Make sure that the pointer being passed in did not
		* come from the xsave buffer itself.
		*/
		WARN_ONCE(xstate_feature_src == dst, "set from xsave buffer itself");

		/* put the caller-provided data in the location */
		memcpy(dst, xstate_feature_src, len);

		/*
		* Mark the xfeature so that the CPU knows there is state
		* in the buffer now.
		*/
		fpu__xfeature_set_non_init(xsave, xstate_feature_mask);
		out:
		/*
		* We are done writing to the 'fpu'. Reenable preeption
		* and (possibly) move the fpstate back in to the fpregs.
		*/
		fpu__current_fpstate_write_end();
		}

		#define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2)
		#define PKRU_VALID_MASK (NR_VALID_PKRU_BITS - 1)

		/*
		* This will go out and modify the XSAVE buffer so that PKRU is
		* set to a particular state for access to 'pkey'.
		*
		* PKRU state does affect kernel access to user memory. We do
		* not modfiy PKRU itself here, only the XSAVE state that will
		* be restored in to PKRU when we return back to userspace.
		* This will go out and modify PKRU register to set the access
		* rights for @pkey to @init_val.
		*/
		int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
		unsigned long init_val)
		{
		struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
		struct pkru_state *old_pkru_state;
		struct pkru_state new_pkru_state;
		u32 old_pkru;
		int pkey_shift = (pkey * PKRU_BITS_PER_PKEY);
		u32 new_pkru_bits = 0;

		@@ -974,6 +886,15 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
		*/
		if (!boot_cpu_has(X86_FEATURE_OSPKE))
		return -EINVAL;
		/*
		* For most XSAVE components, this would be an arduous task:
		* brining fpstate up to date with fpregs, updating fpstate,
		* then re-populating fpregs. But, for components that are
		* never lazily managed, we can just access the fpregs
		* directly. PKRU is never managed lazily, so we can just
		* manipulate it directly. Make sure it stays that way.
		*/
		WARN_ON_ONCE(!use_eager_fpu());

		/* Set the bits we need in PKRU: */
		if (init_val & PKEY_DISABLE_ACCESS)
		@@ -984,37 +905,12 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
		/* Shift the bits in to the correct place in PKRU for pkey: */
		new_pkru_bits <<= pkey_shift;

		/* Locate old copy of the state in the xsave buffer: */
		old_pkru_state = get_xsave_addr(xsave, XFEATURE_MASK_PKRU);

		/*
		* When state is not in the buffer, it is in the init
		* state, set it manually. Otherwise, copy out the old
		* state.
		*/
		if (!old_pkru_state)
		new_pkru_state.pkru = 0;
		else
		new_pkru_state.pkru = old_pkru_state->pkru;

		/* Mask off any old bits in place: */
		new_pkru_state.pkru &= ~((PKRU_AD_BIT\|PKRU_WD_BIT) << pkey_shift);

		/* Set the newly-requested bits: */
		new_pkru_state.pkru \|= new_pkru_bits;

		/*
		* We could theoretically live without zeroing pkru.pad.
		* The current XSAVE feature state definition says that
		* only bytes 0->3 are used. But we do not want to
		* chance leaking kernel stack out to userspace in case a
		* memcpy() of the whole xsave buffer was done.
		*
		* They're in the same cacheline anyway.
		*/
		new_pkru_state.pad = 0;
		/* Get old PKRU and mask off any old bits in place: */
		old_pkru = read_pkru();
		old_pkru &= ~((PKRU_AD_BIT\|PKRU_WD_BIT) << pkey_shift);

		fpu__xfeature_set_state(XFEATURE_MASK_PKRU, &new_pkru_state, sizeof(new_pkru_state));
		/* Write old part along with new part: */
		write_pkru(old_pkru \| new_pkru_bits);

		return 0;
		}

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