FAILED: patch "[PATCH] arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD" failed to apply to 6.1-stable tree

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The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 832dd634bd1b4e3bbe9f10b9c9ba5db6f6f2b97f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024012633-expenses-vastly-81bc@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

832dd634bd1b ("arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD")
546b7cde9b1d ("arm64: Rename ARM64_WORKAROUND_2966298")
471470bc7052 ("arm64: errata: Add Cortex-A520 speculative unprivileged load workaround")
cce8365fc47b ("arm64: errata: Group all Cortex-A510 errata together")
e8069f5a8e3b ("Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 832dd634bd1b4e3bbe9f10b9c9ba5db6f6f2b97f Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Tue, 16 Jan 2024 11:02:20 +0000
Subject: [PATCH] arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD

Currently the ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD workaround isn't
quite right, as it is supposed to be applied after the last explicit
memory access, but is immediately followed by an LDR.

The ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD workaround is used to
handle Cortex-A520 erratum 2966298 and Cortex-A510 erratum 3117295,
which are described in:

* https://developer.arm.com/documentation/SDEN2444153/0600/?lang=en
* https://developer.arm.com/documentation/SDEN1873361/1600/?lang=en

In both cases the workaround is described as:

| If pagetable isolation is disabled, the context switch logic in the
| kernel can be updated to execute the following sequence on affected
| cores before exiting to EL0, and after all explicit memory accesses:
|
| 1. A non-shareable TLBI to any context and/or address, including
|    unused contexts or addresses, such as a `TLBI VALE1 Xzr`.
|
| 2. A DSB NSH to guarantee completion of the TLBI.

The important part being that the TLBI+DSB must be placed "after all
explicit memory accesses".

Unfortunately, as-implemented, the TLBI+DSB is immediately followed by
an LDR, as we have:

| alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
| 	tlbi	vale1, xzr
| 	dsb	nsh
| alternative_else_nop_endif
| alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
| 	ldr	lr, [sp, #S_LR]
| 	add	sp, sp, #PT_REGS_SIZE		// restore sp
| 	eret
| alternative_else_nop_endif
|
| [ ... KPTI exception return path ... ]

This patch fixes this by reworking the logic to place the TLBI+DSB
immediately before the ERET, after all explicit memory accesses.

The ERET is currently in a separate alternative block, and alternatives
cannot be nested. To account for this, the alternative block for
ARM64_UNMAP_KERNEL_AT_EL0 is replaced with a single alternative branch
to skip the KPTI logic, with the new shape of the logic being:

| alternative_insn "b .L_skip_tramp_exit_\@", nop, ARM64_UNMAP_KERNEL_AT_EL0
| 	[ ... KPTI exception return path ... ]
| .L_skip_tramp_exit_\@:
|
| 	ldr	lr, [sp, #S_LR]
| 	add	sp, sp, #PT_REGS_SIZE		// restore sp
|
| alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
| 	tlbi	vale1, xzr
| 	dsb	nsh
| alternative_else_nop_endif
| 	eret

The new structure means that the workaround is only applied when KPTI is
not in use; this is fine as noted in the documented implications of the
erratum:

| Pagetable isolation between EL0 and higher level ELs prevents the
| issue from occurring.

... and as per the workaround description quoted above, the workaround
is only necessary "If pagetable isolation is disabled".

Fixes: 471470bc7052 ("arm64: errata: Add Cortex-A520 speculative unprivileged load workaround")
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Rob Herring <robh@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20240116110221.420467-2-mark.rutland@xxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 544ab46649f3..7fcbee0f6c0e 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -428,16 +428,9 @@ alternative_else_nop_endif
 	ldp	x28, x29, [sp, #16 * 14]
 
 	.if	\el == 0
-alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
-	tlbi	vale1, xzr
-	dsb	nsh
-alternative_else_nop_endif
-alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
-	ldr	lr, [sp, #S_LR]
-	add	sp, sp, #PT_REGS_SIZE		// restore sp
-	eret
-alternative_else_nop_endif
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+	alternative_insn "b .L_skip_tramp_exit_\@", nop, ARM64_UNMAP_KERNEL_AT_EL0
+
 	msr	far_el1, x29
 
 	ldr_this_cpu	x30, this_cpu_vector, x29
@@ -446,7 +439,18 @@ alternative_else_nop_endif
 	ldr		lr, [sp, #S_LR]		// restore x30
 	add		sp, sp, #PT_REGS_SIZE	// restore sp
 	br		x29
+
+.L_skip_tramp_exit_\@:
 #endif
+	ldr	lr, [sp, #S_LR]
+	add	sp, sp, #PT_REGS_SIZE		// restore sp
+
+	/* This must be after the last explicit memory access */
+alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
+	tlbi	vale1, xzr
+	dsb	nsh
+alternative_else_nop_endif
+	eret
 	.else
 	ldr	lr, [sp, #S_LR]
 	add	sp, sp, #PT_REGS_SIZE		// restore sp





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