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| author | Ard Biesheuvel <ardb@kernel.org> | 2023-04-18 17:36:03 +0300 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2023-05-25 18:55:19 +0300 |
| commit | 0936243cabf0caf46f1a42606325ab93cfa05a6a (patch) | |
| tree | bd03ebe84cd1b345bd1393c876645323f1e52d3d /arch/arm64 | |
| parent | 44c026a73be8038f03dbdeef028b642880cf1511 (diff) | |
| download | linux-0936243cabf0caf46f1a42606325ab93cfa05a6a.tar.xz | |
arm64: entry: Preserve/restore X29 even for compat tasks
Currently, the KPTI trampoline code for returning to user space takes
care to only preserve X29 into FAR_EL1 for native tasks, as compat tasks
don't have access to this register anyway, and so preserving it is not
necessary. It also means it does not need to be restored, and so we have
two code paths for returning back to user space: the native one that
restores X29 from FAR_EL1, and the compat one that leaves X29 clobbered,
containing the value of TTBR1_EL1, which carries a physical address
pointing somewhere into the kernel image.
This is needlessly complex, and given that FAR_EL1 becomes UNKNOWN after
an exception return anway, the only benefit of avoiding the preserve and
restore is that we can skip the system register write and read.
So let's simplify this, and collapse the two code paths into one that
always preserves X29 into FAR_EL1, and always restores it again after
the TTBR switch.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230418143604.1176437-2-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64')
| -rw-r--r-- | arch/arm64/kernel/entry.S | 10 |
1 files changed, 0 insertions, 10 deletions
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index ab2a6e33c052..16fbd0d9790d 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -435,13 +435,9 @@ alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0 eret alternative_else_nop_endif #ifdef CONFIG_UNMAP_KERNEL_AT_EL0 - bne 4f msr far_el1, x29 tramp_alias x30, tramp_exit_native, x29 br x30 -4: - tramp_alias x30, tramp_exit_compat, x29 - br x30 #endif .else ldr lr, [sp, #S_LR] @@ -740,9 +736,7 @@ alternative_else_nop_endif msr vbar_el1, x30 ldr lr, [sp, #S_LR] tramp_unmap_kernel x29 - .if \regsize == 64 mrs x29, far_el1 - .endif add sp, sp, #PT_REGS_SIZE // restore sp eret sb @@ -780,10 +774,6 @@ SYM_CODE_END(tramp_vectors) SYM_CODE_START(tramp_exit_native) tramp_exit SYM_CODE_END(tramp_exit_native) - -SYM_CODE_START(tramp_exit_compat) - tramp_exit 32 -SYM_CODE_END(tramp_exit_compat) .popsection // .entry.tramp.text #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */ |