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

[Alexandre Ghiti]

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>
---
 arch/riscv/kernel/vendor_extensions.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/vendor_extensions.c b/arch/riscv/kernel/vendor_extensions.c
index b6c1e7b5d34b..01dc79b1d17b 100644
--- a/arch/riscv/kernel/vendor_extensions.c
+++ b/arch/riscv/kernel/vendor_extensions.c
@@ -27,7 +27,7 @@ const size_t riscv_isa_vendor_ext_list_size = ARRAY_SIZE(riscv_isa_vendor_ext_li
  * @bit: bit position of the desired extension
  * Return: true or false
  *
- * NOTE: When cpu is -1, will check if extension is available on all cpus
+ * NOTE: When cpu is VENDOR_EXT_ALL_CPUS, will check if extension is available on all cpus
  */
 bool __riscv_isa_vendor_extension_available(int cpu, unsigned long vendor, unsigned int bit)
 {
@@ -38,14 +38,15 @@ bool __riscv_isa_vendor_extension_available(int cpu, unsigned long vendor, unsig
 	#ifdef CONFIG_RISCV_ISA_VENDOR_EXT_ANDES
 	case ANDES_VENDOR_ID:
 		bmap = &riscv_isa_vendor_ext_list_andes.all_harts_isa_bitmap;
-		cpu_bmap = &riscv_isa_vendor_ext_list_andes.per_hart_isa_bitmap[cpu];
+		if (cpu != VENDOR_EXT_ALL_CPUS)
+			cpu_bmap = &riscv_isa_vendor_ext_list_andes.per_hart_isa_bitmap[cpu];
 		break;
 	#endif
 	default:
 		return false;
 	}
 
-	if (cpu != -1)
+	if (cpu != VENDOR_EXT_ALL_CPUS)
 		bmap = &cpu_bmap[cpu];
 
 	if (bit >= RISCV_ISA_VENDOR_EXT_MAX)
-- 
2.39.2