[PATCH] powerpc/ftrace: Ignore ftrace locations in exit text sections
Christophe Leroy
christophe.leroy at csgroup.eu
Tue Feb 13 06:31:03 AEDT 2024
Le 09/02/2024 à 08:59, Naveen N Rao a écrit :
> Michael reported that we are seeing ftrace bug on bootup when KASAN is
> enabled, and if we are using -fpatchable-function-entry:
>
> ftrace: allocating 47780 entries in 18 pages
> ftrace-powerpc: 0xc0000000020b3d5c: No module provided for non-kernel address
> ------------[ ftrace bug ]------------
> ftrace faulted on modifying
> [<c0000000020b3d5c>] 0xc0000000020b3d5c
> Initializing ftrace call sites
> ftrace record flags: 0
> (0)
> expected tramp: c00000000008cef4
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:2180 ftrace_bug+0x3c0/0x424
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 6.5.0-rc3-00120-g0f71dcfb4aef #860
> Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
> NIP: c0000000003aa81c LR: c0000000003aa818 CTR: 0000000000000000
> REGS: c0000000033cfab0 TRAP: 0700 Not tainted (6.5.0-rc3-00120-g0f71dcfb4aef)
> MSR: 8000000002021033 <SF,VEC,ME,IR,DR,RI,LE> CR: 28028240 XER: 00000000
> CFAR: c0000000002781a8 IRQMASK: 3
> ...
> NIP [c0000000003aa81c] ftrace_bug+0x3c0/0x424
> LR [c0000000003aa818] ftrace_bug+0x3bc/0x424
> Call Trace:
> ftrace_bug+0x3bc/0x424 (unreliable)
> ftrace_process_locs+0x5f4/0x8a0
> ftrace_init+0xc0/0x1d0
> start_kernel+0x1d8/0x484
>
> With CONFIG_FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY=y and
> CONFIG_KASAN=y, compiler emits nops in functions that it generates for
> registering and unregistering global variables (unlike with -pg and
> -mprofile-kernel where calls to _mcount() are not generated in those
> functions). Those functions then end up in INIT_TEXT and EXIT_TEXT
> respectively. We don't expect to see any profiled functions in
> EXIT_TEXT, so ftrace_init_nop() assumes that all addresses that aren't
> in the core kernel text belongs to a module. Since these functions do
> not match that criteria, we see the above bug.
>
> Address this by having ftrace ignore all locations in the text exit
> sections of vmlinux.
>
> Fixes: 0f71dcfb4aef ("powerpc/ftrace: Add support for -fpatchable-function-entry")
> Cc: stable at vger.kernel.org
> Reported-by: Michael Ellerman <mpe at ellerman.id.au>
> Signed-off-by: Naveen N Rao <naveen at kernel.org>
> ---
> arch/powerpc/include/asm/ftrace.h | 9 +--------
> arch/powerpc/include/asm/sections.h | 1 +
> arch/powerpc/kernel/trace/ftrace.c | 12 ++++++++++++
> arch/powerpc/kernel/vmlinux.lds.S | 2 ++
> 4 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index 1ebd2ca97f12..d6babd083202 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -20,14 +20,7 @@
> #ifndef __ASSEMBLY__
> extern void _mcount(void);
>
> -static inline unsigned long ftrace_call_adjust(unsigned long addr)
> -{
> - if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
> - addr += MCOUNT_INSN_SIZE;
> -
> - return addr;
> -}
> -
> +unsigned long ftrace_call_adjust(unsigned long addr);
> unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
> unsigned long sp);
>
> diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
> index ea26665f82cf..d389dcecdb0b 100644
> --- a/arch/powerpc/include/asm/sections.h
> +++ b/arch/powerpc/include/asm/sections.h
> @@ -14,6 +14,7 @@ typedef struct func_desc func_desc_t;
>
> extern char __head_end[];
> extern char __srwx_boundary[];
> +extern char _sexittext[], _eexittext[];
Should we try to at least use the same symbols as others, or best try to
move this into include/asm-generic/sections.h, just like inittext ?
$ git grep exittext
arch/arm64/include/asm/sections.h:extern char __exittext_begin[],
__exittext_end[];
arch/arm64/kernel/patching.c: addr >= (unsigned
long)__exittext_begin &&
arch/arm64/kernel/patching.c: addr < (unsigned
long)__exittext_end;
arch/arm64/kernel/vmlinux.lds.S: __exittext_begin = .;
arch/arm64/kernel/vmlinux.lds.S: __exittext_end = .;
arch/riscv/include/asm/sections.h:extern char __exittext_begin[],
__exittext_end[];
arch/riscv/kernel/patch.c:static inline bool
is_kernel_exittext(uintptr_t addr)
arch/riscv/kernel/patch.c: addr >=
(uintptr_t)__exittext_begin &&
arch/riscv/kernel/patch.c: addr < (uintptr_t)__exittext_end;
arch/riscv/kernel/patch.c: if (core_kernel_text(uintaddr) ||
is_kernel_exittext(uintaddr))
arch/riscv/kernel/vmlinux-xip.lds.S: __exittext_begin = .;
arch/riscv/kernel/vmlinux-xip.lds.S: __exittext_end = .;
arch/riscv/kernel/vmlinux.lds.S: __exittext_begin = .;
arch/riscv/kernel/vmlinux.lds.S: __exittext_end = .;
>
> /* Patch sites */
> extern s32 patch__call_flush_branch_caches1;
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 82010629cf88..b5efd8d7bc01 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -27,10 +27,22 @@
> #include <asm/ftrace.h>
> #include <asm/syscall.h>
> #include <asm/inst.h>
> +#include <asm/sections.h>
>
> #define NUM_FTRACE_TRAMPS 2
> static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS];
>
> +unsigned long ftrace_call_adjust(unsigned long addr)
> +{
> + if (addr >= (unsigned long)_sexittext && addr < (unsigned long)_eexittext)
> + return 0;
Then arm64 has a function called is_exit_text() and riscv has
is_kernel_exittext(). Can we refactor ?
> +
> + if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
> + addr += MCOUNT_INSN_SIZE;
> +
> + return addr;
> +}
> +
> static ppc_inst_t ftrace_create_branch_inst(unsigned long ip, unsigned long addr, int link)
> {
> ppc_inst_t op;
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index 1c5970df3233..9c376ae6857d 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -281,7 +281,9 @@ SECTIONS
> * to deal with references from __bug_table
> */
> .exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) {
> + _sexittext = .;
> EXIT_TEXT
> + _eexittext = .;
> }
>
> . = ALIGN(PAGE_SIZE);
>
> base-commit: 4ef8376c466ae8b03e632dd8eca1e44315f7dd61
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