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arm64: fpsimd: Fix type mismatch in sme_{save,load}_state()

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The sme_save_state() and sme_load_state() functions take a 32-bit int
argument that describes whether to save/restore ZT0. Their assembly
implementations consume the entire 64-bit register containing this
32-bit value, and will attempt to save/restore ZT0 if any bit of
that 64-bit register is non-zero.

Per the AAPCS64 parameter passing rules, the callee is responsible for
any necessary widening, and the upper 32-bits are permitted to contain
arbitrary values. If the upper 32 bits are non-zero, this could result
in an unexpected attempt to save/restore ZT0, and consequently could
lead to unexpected traps/undefs/faults.

In practice compilers are very unlikely to generate code where the upper
32-bits would be non-zero, but they are permitted to do so.

Fix this by only consuming the low 32 bits of the register, and update
comments accordingly.

Fixes: 95fcec7132 ("arm64/sme: Implement context switching for ZT0")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2026-06-03 12:06:12 +01:00 committed by Will Deacon
parent ae24f6b06e
commit 247bd15390
1 changed files with 4 additions and 4 deletions
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8
arch/arm64/kernel/entry-fpsimd.S
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@ -103,13 +103,13 @@ SYM_FUNC_END(sme_set_vq)
* Save the ZA and ZT state
*
* x0 - pointer to buffer for state
* x1 - number of ZT registers to save
* w1 - number of ZT registers to save
*/
SYM_FUNC_START(sme_save_state)
_sme_rdsvl 2, 1 // x2 = VL/8
sme_save_za 0, x2, 12 // Leaves x0 pointing to the end of ZA
cbz x1, 1f
cbz w1, 1f
_str_zt 0
1:
ret
@ -119,13 +119,13 @@ SYM_FUNC_END(sme_save_state)
* Load the ZA and ZT state
*
* x0 - pointer to buffer for state
* x1 - number of ZT registers to save
* w1 - number of ZT registers to save
*/
SYM_FUNC_START(sme_load_state)
_sme_rdsvl 2, 1 // x2 = VL/8
sme_load_za 0, x2, 12 // Leaves x0 pointing to the end of ZA
cbz x1, 1f
cbz w1, 1f
_ldr_zt 0
1:
ret