6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ard Biesheuvel ardb@kernel.org
[ Upstream commit 73cfc53cc3b6380eccf013049574485f64cb83ca ]
A C jump table (such as the one used by the BPF interpreter) is a const global array of absolute code addresses, and this means that the actual values in the table may not be known until the kernel is booted (e.g., when using KASLR or when the kernel VA space is sized dynamically).
When using PIE codegen, the compiler will default to placing such const global objects in .data.rel.ro (which is annotated as writable), rather than .rodata (which is annotated as read-only). As C jump tables are explicitly emitted into .rodata, this used to result in warnings for LoongArch builds (which uses PIE codegen for the entire kernel) like
Warning: setting incorrect section attributes for .rodata..c_jump_table
due to the fact that the explicitly specified .rodata section inherited the read-write annotation that the compiler uses for such objects when using PIE codegen.
This warning was suppressed by explicitly adding the read-only annotation to the __attribute__((section(""))) string, by commit
c5b1184decc8 ("compiler.h: specify correct attribute for .rodata..c_jump_table")
Unfortunately, this hack does not work on Clang's integrated assembler, which happily interprets the appended section type and permission specifiers as part of the section name, which therefore no longer matches the hard-coded pattern '.rodata..c_jump_table' that objtool expects, causing it to emit a warning
kernel/bpf/core.o: warning: objtool: ___bpf_prog_run+0x20: sibling call from callable instruction with modified stack frame
Work around this, by emitting C jump tables into .data.rel.ro instead, which is treated as .rodata by the linker script for all builds, not just PIE based ones.
Fixes: c5b1184decc8 ("compiler.h: specify correct attribute for .rodata..c_jump_table") Tested-by: Tiezhu Yang yangtiezhu@loongson.cn # on LoongArch Signed-off-by: Ard Biesheuvel ardb@kernel.org Link: https://lore.kernel.org/r/20250221135704.431269-6-ardb+git@google.com Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/compiler.h | 2 +- tools/objtool/check.c | 7 ++++--- tools/objtool/include/objtool/special.h | 2 +- 3 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 75a83394824c4..b15911e201bf9 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -110,7 +110,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, /* Unreachable code */ #ifdef CONFIG_OBJTOOL /* Annotate a C jump table to allow objtool to follow the code flow */ -#define __annotate_jump_table __section(".rodata..c_jump_table,"a",@progbits #") +#define __annotate_jump_table __section(".data.rel.ro.c_jump_table") #else /* !CONFIG_OBJTOOL */ #define __annotate_jump_table #endif /* CONFIG_OBJTOOL */ diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 3e72c9f9b7f37..1691aa6e6ce32 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2589,13 +2589,14 @@ static void mark_rodata(struct objtool_file *file) * * - .rodata: can contain GCC switch tables * - .rodata.<func>: same, if -fdata-sections is being used - * - .rodata..c_jump_table: contains C annotated jump tables + * - .data.rel.ro.c_jump_table: contains C annotated jump tables * * .rodata.str1.* sections are ignored; they don't contain jump tables. */ for_each_sec(file, sec) { - if (!strncmp(sec->name, ".rodata", 7) && - !strstr(sec->name, ".str1.")) { + if ((!strncmp(sec->name, ".rodata", 7) && + !strstr(sec->name, ".str1.")) || + !strncmp(sec->name, ".data.rel.ro", 12)) { sec->rodata = true; found = true; } diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h index 86d4af9c5aa9d..89ee12b1a1384 100644 --- a/tools/objtool/include/objtool/special.h +++ b/tools/objtool/include/objtool/special.h @@ -10,7 +10,7 @@ #include <objtool/check.h> #include <objtool/elf.h>
-#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table" +#define C_JUMP_TABLE_SECTION ".data.rel.ro.c_jump_table"
struct special_alt { struct list_head list;