x86/cpu: Use pinning mask for CR4 bits needing to be 0
commit a13b9d0b97
upstream.
The X86_CR4_FSGSBASE bit of CR4 should not change after boot[1]. Older
kernels should enforce this bit to zero, and newer kernels need to
enforce it depending on boot-time configuration (e.g. "nofsgsbase").
To support a pinned bit being either 1 or 0, use an explicit mask in
combination with the expected pinned bit values.
[1] https://lore.kernel.org/lkml/20200527103147.GI325280@hirez.programming.kicks-ass.net
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/202006082013.71E29A42@keescook
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
5.4-rM2-2.2.x-imx-squashed
parent
96a8013355
commit
3ceaf206b7
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@ -366,6 +366,9 @@ out:
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cr4_clear_bits(X86_CR4_UMIP);
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}
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/* These bits should not change their value after CPU init is finished. */
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static const unsigned long cr4_pinned_mask =
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X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP | X86_CR4_FSGSBASE;
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static DEFINE_STATIC_KEY_FALSE_RO(cr_pinning);
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static unsigned long cr4_pinned_bits __ro_after_init;
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@ -390,20 +393,20 @@ EXPORT_SYMBOL(native_write_cr0);
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void native_write_cr4(unsigned long val)
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{
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unsigned long bits_missing = 0;
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unsigned long bits_changed = 0;
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set_register:
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asm volatile("mov %0,%%cr4": "+r" (val), "+m" (cr4_pinned_bits));
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if (static_branch_likely(&cr_pinning)) {
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if (unlikely((val & cr4_pinned_bits) != cr4_pinned_bits)) {
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bits_missing = ~val & cr4_pinned_bits;
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val |= bits_missing;
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if (unlikely((val & cr4_pinned_mask) != cr4_pinned_bits)) {
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bits_changed = (val & cr4_pinned_mask) ^ cr4_pinned_bits;
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val = (val & ~cr4_pinned_mask) | cr4_pinned_bits;
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goto set_register;
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}
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/* Warn after we've set the missing bits. */
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WARN_ONCE(bits_missing, "CR4 bits went missing: %lx!?\n",
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bits_missing);
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/* Warn after we've corrected the changed bits. */
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WARN_ONCE(bits_changed, "pinned CR4 bits changed: 0x%lx!?\n",
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bits_changed);
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}
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}
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EXPORT_SYMBOL(native_write_cr4);
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@ -415,7 +418,7 @@ void cr4_init(void)
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if (boot_cpu_has(X86_FEATURE_PCID))
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cr4 |= X86_CR4_PCIDE;
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if (static_branch_likely(&cr_pinning))
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cr4 |= cr4_pinned_bits;
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cr4 = (cr4 & ~cr4_pinned_mask) | cr4_pinned_bits;
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__write_cr4(cr4);
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@ -430,10 +433,7 @@ void cr4_init(void)
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*/
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static void __init setup_cr_pinning(void)
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{
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unsigned long mask;
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mask = (X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP);
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cr4_pinned_bits = this_cpu_read(cpu_tlbstate.cr4) & mask;
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cr4_pinned_bits = this_cpu_read(cpu_tlbstate.cr4) & cr4_pinned_mask;
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static_key_enable(&cr_pinning.key);
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}
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