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From foo@baz Tue Mar 8 08:47:19 PM CET 2022 |
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From: James Morse <james.morse@arm.com> |
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Date: Tue, 23 Nov 2021 18:41:43 +0000 |
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Subject: arm64: entry: Free up another register on kpti's tramp_exit path |
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From: James Morse <james.morse@arm.com> |
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commit 03aff3a77a58b5b52a77e00537a42090ad57b80b upstream. |
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Kpti stashes x30 in far_el1 while it uses x30 for all its work. |
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|
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Making the vectors a per-cpu data structure will require a second |
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register. |
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|
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Allow tramp_exit two registers before it unmaps the kernel, by |
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leaving x30 on the stack, and stashing x29 in far_el1. |
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|
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Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> |
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Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> |
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Signed-off-by: James Morse <james.morse@arm.com> |
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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--- |
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arch/arm64/kernel/entry.S | 19 +++++++++++++------ |
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1 file changed, 13 insertions(+), 6 deletions(-) |
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|
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--- a/arch/arm64/kernel/entry.S |
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+++ b/arch/arm64/kernel/entry.S |
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@@ -419,14 +419,16 @@ alternative_else_nop_endif |
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ldp x24, x25, [sp, #16 * 12] |
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ldp x26, x27, [sp, #16 * 13] |
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ldp x28, x29, [sp, #16 * 14] |
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- ldr lr, [sp, #S_LR] |
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- add sp, sp, #PT_REGS_SIZE // restore sp |
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|
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.if \el == 0 |
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-alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0 |
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+alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0 |
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+ ldr lr, [sp, #S_LR] |
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+ add sp, sp, #PT_REGS_SIZE // restore sp |
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+ eret |
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+alternative_else_nop_endif |
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#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 |
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bne 4f |
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- msr far_el1, x30 |
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+ msr far_el1, x29 |
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tramp_alias x30, tramp_exit_native |
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br x30 |
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4: |
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@@ -434,6 +436,9 @@ alternative_insn eret, nop, ARM64_UNMAP_ |
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br x30 |
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#endif |
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.else |
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+ ldr lr, [sp, #S_LR] |
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+ add sp, sp, #PT_REGS_SIZE // restore sp |
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+ |
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/* Ensure any device/NC reads complete */ |
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alternative_insn nop, "dmb sy", ARM64_WORKAROUND_1508412 |
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|
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@@ -674,10 +679,12 @@ alternative_else_nop_endif |
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.macro tramp_exit, regsize = 64 |
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adr x30, tramp_vectors |
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msr vbar_el1, x30 |
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- tramp_unmap_kernel x30 |
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+ ldr lr, [sp, #S_LR] |
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+ tramp_unmap_kernel x29 |
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.if \regsize == 64 |
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- mrs x30, far_el1 |
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+ mrs x29, far_el1 |
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.endif |
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+ add sp, sp, #PT_REGS_SIZE // restore sp |
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eret |
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sb |
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.endm |
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