[PATCH -fixes] riscv: Fix out-of-bounds when accessing Andes per hart vendor extension array

[Conor Dooley]

On Sun, Aug 11, 2024 at 05:02:29PM +0200, Alexandre Ghiti wrote:
> The out-of-bounds access is reported by UBSAN:
> 
> [    0.000000] UBSAN: array-index-out-of-bounds in ../arch/riscv/kernel/vendor_extensions.c:41:66
> [    0.000000] index -1 is out of range for type 'riscv_isavendorinfo [32]'
> [    0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.11.0-rc2ubuntu-defconfig #2
> [    0.000000] Hardware name: riscv-virtio,qemu (DT)
> [    0.000000] Call Trace:
> [    0.000000] [<ffffffff94e078ba>] dump_backtrace+0x32/0x40
> [    0.000000] [<ffffffff95c83c1a>] show_stack+0x38/0x44
> [    0.000000] [<ffffffff95c94614>] dump_stack_lvl+0x70/0x9c
> [    0.000000] [<ffffffff95c94658>] dump_stack+0x18/0x20
> [    0.000000] [<ffffffff95c8bbb2>] ubsan_epilogue+0x10/0x46
> [    0.000000] [<ffffffff95485a82>] __ubsan_handle_out_of_bounds+0x94/0x9c
> [    0.000000] [<ffffffff94e09442>] __riscv_isa_vendor_extension_available+0x90/0x92
> [    0.000000] [<ffffffff94e043b6>] riscv_cpufeature_patch_func+0xc4/0x148
> [    0.000000] [<ffffffff94e035f8>] _apply_alternatives+0x42/0x50
> [    0.000000] [<ffffffff95e04196>] apply_boot_alternatives+0x3c/0x100
> [    0.000000] [<ffffffff95e05b52>] setup_arch+0x85a/0x8bc
> [    0.000000] [<ffffffff95e00ca0>] start_kernel+0xa4/0xfb6
> 
> This happens because we unconditionally use the cpu parameter to access
> this array. But if -1 is passed, that means we should not and we don't
> need to access this array, so simply prevent accessing the array in that case.
> 
> Fixes: 23c996fc2bc1 ("riscv: Extend cpufeature.c to detect vendor extensions")
> Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>

Tested-by: Conor Dooley <conor.dooley at microchip.com>
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