Merge pull request #527 from mkroening/xcr0-update

feat: add `update()` to `Cr3`, `Dr7`, `SFMask`, `UCet`, `SCet`, `mxcsr`, `rflags`, and `XCr0`

src/registers/control.rs

@@ -361,6 +361,63 @@ mod x86_64 {
                 asm!("mov cr3, {}", in(reg) value, options(nostack, preserves_flags));
             }
         }
+
+        /// Update the P4 table address in the CR3 register.
+        ///
+        /// ## Safety
+        ///
+        /// Changing the level 4 page table is unsafe, because it's possible to violate memory safety by
+        /// changing the page mapping.
+        #[inline]
+        pub unsafe fn update<F>(f: F)
+        where
+            F: FnOnce(&mut PhysFrame, &mut Cr3Flags),
+        {
+            let (mut frame, mut flags) = Self::read();
+            f(&mut frame, &mut flags);
+            unsafe {
+                Self::write(frame, flags);
+            }
+        }
+
+        /// Updates the P4 table address in the CR3 register.
+        ///
+        /// ## Safety
+        ///
+        /// Changing the level 4 page table is unsafe, because it's possible to violate memory safety by
+        /// changing the page mapping.
+        /// [`Cr4Flags::PCID`] must be set before calling this method.
+        #[inline]
+        pub unsafe fn update_pcid<F>(f: F)
+        where
+            F: FnOnce(&mut PhysFrame, &mut Pcid),
+        {
+            let (mut frame, mut pcid) = Self::read_pcid();
+            f(&mut frame, &mut pcid);
+            unsafe {
+                Self::write_pcid(frame, pcid);
+            }
+        }
+
+        /// Updates the P4 table address in the CR3 register without flushing existing TLB entries for
+        /// the PCID.
+        ///
+        /// ## Safety
+        ///
+        /// Changing the level 4 page table is unsafe, because it's possible to violate memory safety by
+        /// changing the page mapping.
+        /// [`Cr4Flags::PCID`] must be set before calling this method.
+        #[inline]
+        pub unsafe fn update_pcid_no_flush<F>(f: F)
+        where
+            F: FnOnce(&mut PhysFrame, &mut Pcid),
+        {
+            let (mut frame, mut pcid) = Self::read_pcid();
+            f(&mut frame, &mut pcid);
+            unsafe {
+                Self::write_pcid_no_flush(frame, pcid);
+            }
+        }
     }
 
     impl Cr4 {

src/registers/debug.rs

@@ -499,5 +499,18 @@ mod x86_64 {
                 asm!("mov dr7, {}", in(reg) value, options(nomem, nostack, preserves_flags));
             }
         }
+
+        /// Update the DR7 value.
+        ///
+        /// Preserves the value of reserved fields.
+        #[inline]
+        pub fn update<F>(f: F)
+        where
+            F: FnOnce(&mut Dr7Value),
+        {
+            let mut value = Self::read();
+            f(&mut value);
+            Self::write(value);
+        }
     }
 }

src/registers/model_specific.rs

@@ -525,6 +525,24 @@ mod x86_64 {
             let mut msr = Self::MSR;
             unsafe { msr.write(value.bits()) };
         }
+
+        /// Update the SFMask register.
+        ///
+        /// The SFMASK register is used to specify which RFLAGS bits
+        /// are cleared during a SYSCALL. In long mode, SFMASK is used
+        /// to specify which RFLAGS bits are cleared when SYSCALL is
+        /// executed. If a bit in SFMASK is set to 1, the corresponding
+        /// bit in RFLAGS is cleared to 0. If a bit in SFMASK is cleared
+        /// to 0, the corresponding rFLAGS bit is not modified.
+        #[inline]
+        pub fn update<F>(f: F)
+        where
+            F: FnOnce(&mut RFlags),
+        {
+            let mut flags = Self::read();
+            f(&mut flags);
+            Self::write(flags);
+        }
     }
 
     impl UCet {
@@ -560,6 +578,17 @@ mod x86_64 {
         pub fn write(flags: CetFlags, legacy_bitmap: Page) {
             Self::write_raw(flags.bits() | legacy_bitmap.start_address().as_u64());
         }
+
+        /// Updates IA32_U_CET.
+        #[inline]
+        pub fn update<F>(f: F)
+        where
+            F: FnOnce(&mut CetFlags, &mut Page),
+        {
+            let (mut flags, mut legacy_bitmap) = Self::read();
+            f(&mut flags, &mut legacy_bitmap);
+            Self::write(flags, legacy_bitmap);
+        }
     }
 
     impl SCet {
@@ -595,5 +624,16 @@ mod x86_64 {
         pub fn write(flags: CetFlags, legacy_bitmap: Page) {
             Self::write_raw(flags.bits() | legacy_bitmap.start_address().as_u64());
         }
+
+        /// Updates IA32_S_CET.
+        #[inline]
+        pub fn update<F>(f: F)
+        where
+            F: FnOnce(&mut CetFlags, &mut Page),
+        {
+            let (mut flags, mut legacy_bitmap) = Self::read();
+            f(&mut flags, &mut legacy_bitmap);
+            Self::write(flags, legacy_bitmap);
+        }
     }
 }

src/registers/mxcsr.rs

@@ -83,6 +83,17 @@ mod x86_64 {
         }
     }
 
+    /// Update MXCSR.
+    #[inline]
+    pub fn update<F>(f: F)
+    where
+        F: FnOnce(&mut MxCsr),
+    {
+        let mut mxcsr = self::read();
+        f(&mut mxcsr);
+        self::write(mxcsr);
+    }
+
     #[cfg(test)]
     mod test {
         use crate::registers::mxcsr::*;

src/registers/rflags.rs

@@ -126,6 +126,25 @@ mod x86_64 {
         }
     }
 
+    /// Updates the RFLAGS register, preserves reserved bits.
+    ///
+    /// ## Safety
+    ///
+    /// Unsafe because undefined becavior can occur if certain flags are modified. For example,
+    /// the `DF` flag must be unset in all Rust code. Also, modifying `CF`, `PF`, or any other
+    /// flags also used by Rust/LLVM can result in undefined behavior too.
+    #[inline]
+    pub unsafe fn update<F>(f: F)
+    where
+        F: FnOnce(&mut RFlags),
+    {
+        let mut flags = self::read();
+        f(&mut flags);
+        unsafe {
+            self::write(flags);
+        }
+    }
+
     #[cfg(test)]
     mod test {
         use crate::registers::rflags::read;

src/registers/xcontrol.rs

@@ -85,7 +85,7 @@ mod x86_64 {
         /// ## Safety
         ///
         /// This function is unsafe because it's possible to
-        /// enable features that are not supported by the architecture
+        /// enable features that are not supported by the architecture.
         #[inline]
         pub unsafe fn write(flags: XCr0Flags) {
             let old_value = Self::read_raw();
@@ -145,5 +145,26 @@ mod x86_64 {
                 );
             }
         }
+
+        /// Update XCR0 flags.
+        ///
+        /// Preserves the value of reserved fields.
+        /// Panics if invalid combinations of [`XCr0Flags`] are set.
+        ///
+        /// ## Safety
+        ///
+        /// This function is unsafe because it's possible to
+        /// enable features that are not supported by the architecture.
+        #[inline]
+        pub unsafe fn update<F>(f: F)
+        where
+            F: FnOnce(&mut XCr0Flags),
+        {
+            let mut flags = Self::read();
+            f(&mut flags);
+            unsafe {
+                Self::write(flags);
+            }
+        }
     }
 }