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authorMark Brown <broonie@kernel.org>2024-01-15 21:42:38 +0300
committerWill Deacon <will@kernel.org>2024-01-18 14:04:17 +0300
commitb7c510d049049409e8945b932f4b0b357fa17415 (patch)
tree429d149fc34f86c1b12ae54a3d3257d70f3b86ed /arch
parentda59f1d051d57e85eca49401a3a36d5a622babde (diff)
downloadlinux-b7c510d049049409e8945b932f4b0b357fa17415.tar.xz
arm64/ptrace: Don't flush ZA/ZT storage when writing ZA via ptrace
When writing ZA we currently unconditionally flush the buffer used to store it as part of ensuring that it is allocated. Since this buffer is shared with ZT0 this means that a write to ZA when PSTATE.ZA is already set will corrupt the value of ZT0 on a SME2 system. Fix this by only flushing the backing storage if PSTATE.ZA was not previously set. This will mean that short or failed writes may leave stale data in the buffer, this seems as correct as our current behaviour and unlikely to be something that userspace will rely on. Fixes: f90b529bcbe5 ("arm64/sme: Implement ZT0 ptrace support") Signed-off-by: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20240115-arm64-fix-ptrace-za-zt-v1-1-48617517028a@kernel.org Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/kernel/ptrace.c13
1 files changed, 7 insertions, 6 deletions
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 20d7ef82de90..b3f64144b5cd 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1107,12 +1107,13 @@ static int za_set(struct task_struct *target,
}
}
- /* Allocate/reinit ZA storage */
- sme_alloc(target, true);
- if (!target->thread.sme_state) {
- ret = -ENOMEM;
- goto out;
- }
+ /*
+ * Only flush the storage if PSTATE.ZA was not already set,
+ * otherwise preserve any existing data.
+ */
+ sme_alloc(target, !thread_za_enabled(&target->thread));
+ if (!target->thread.sme_state)
+ return -ENOMEM;
/* If there is no data then disable ZA */
if (!count) {