riscv: patch: fix handling of bpf-jit execmem addresses

Commit 8718e5a309 ("riscv: patch: skip fixmap mapping when kernel text
is already writable") gated the core_kernel_text() branch of patch_map()
on CONFIG_STRICT_KERNEL_RWX, and explicitly left the vmalloc branch
unchanged. That branch has a separate problem.

That branch only creates a temporary writable fixmap alias when
CONFIG_STRICT_MODULE_RWX is enabled, and otherwise assumes the target is
directly writable and returns the address unchanged. That assumption no
longer holds: bpf_prog_pack_alloc calls set_memory_rox() on every pack
unconditionally in alloc_new_pack(), independently of any
CONFIG_STRICT_*_RWX option, so BPF text in the vmalloc area is read-only
regardless of what CONFIG_STRICT_MODULE_RWX says.

With CONFIG_STRICT_MODULE_RWX=n, patch_map() returns the read-only
address directly, the subsequent copy_to_kernel_nofault() takes a
page fault and returns -EFAULT. bpf_arch_text_copy() turns that into
-EINVAL, which propagates through bpf_jit_binary_pack_finalize() to the
WARN_ON() in bpf_int_jit_compile() and leaves the program un-JITed.

Note that BPF cannot be fixed the way kprobes was in
commit bdc46e507b ("riscv: mm: make EXECMEM_KPROBES writable without
CONFIG_STRICT_MODULE_RWX"). EXECMEM_BPF is already PAGE_KERNEL, i.e.
writable at allocation time; the read-only mapping is established
afterwards by generic code in alloc_new_pack(), which arch code cannot
influence. The only place this can be handled is patch_map().

This is the same problem that was fixed on arm64 by commit b1480ed230
("arm64: patching: fix handling of execmem addresses"), and the fix is
the same: CONFIG_EXECMEM is what actually tracks whether the vmalloc
area can hold executable memory that needs a temporary alias to be
written. CONFIG_BPF_JIT, CONFIG_KPROBES and CONFIG_MODULES all select
it.

Note that this is not limited to CONFIG_MODULES=n. Unlike arm64, riscv
selects CONFIG_ARCH_OPTIONAL_KERNEL_RWX, so CONFIG_STRICT_MODULE_RWX can
be disabled with CONFIG_MODULES=y as well, and the bug is reachable in
that configuration too.

The !CONFIG_MMU build is unaffected: it has its own __patch_insn_set()
and __patch_insn_write() implementations and never calls patch_map().

Fixes: 2c9e5d4a00 ("bpf: remove CONFIG_BPF_JIT dependency on CONFIG_MODULES of")
Signed-off-by: Wei-Jie Hung <imbigking12@gmail.com>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Tested-by: Pu Lehui <pulehui@huawei.com>
Link: https://patch.msgid.link/20260914115607.350097-1-imbigking12@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Paul Walmsley <pjw@kernel.org>

arch/riscv/kernel/patch.c

@@ -48,7 +48,7 @@ static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
 		if (!IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
 			return addr;
 		phys = __pa_symbol(addr);
-	} else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) {
+	} else if (IS_ENABLED(CONFIG_EXECMEM)) {
 		struct page *page = vmalloc_to_page(addr);
 
 		BUG_ON(!page);