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Message-Id: <20241029-arm-generic-entry-v2-9-573519abef38@linaro.org>
Date: Tue, 29 Oct 2024 11:52:49 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Oleg Nesterov <oleg@...hat.com>, Russell King <linux@...linux.org.uk>,
Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...capital.net>,
Will Drewry <wad@...omium.org>, Frederic Weisbecker <frederic@...nel.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Jinjie Ruan <ruanjinjie@...wei.com>, Arnd Bergmann <arnd@...db.de>,
Ard Biesheuvel <ardb@...nel.org>, Al Viro <viro@...iv.linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH RFC v2 09/28] ARM: entry: save the syscall sp in
thread_info
We are going to rewrite the syscall handling in C, which
means that the stack used by the call code is no longer
predicatably 8 bytes (for syscall arguments r4 and r5)
but a varying number of bytes depending on how nested the
C code is.
However the current code is just assuming it can rewind
the stack by adding 8 to sp if a syscall is interrupted by
a sigreturn call.
Solve this by storing the entry sp in the per-task
struct thread_info and use that in the sigreturn wrapper
instead. We already have the thread info available in
the SWI entry and sigreturn is probably not so common
that retrieveing a pointer to thread_info should affect
anything very much.
Storing this per-task in thread_info makes the solution
SMP robust.
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
arch/arm/include/asm/thread_info.h | 1 +
arch/arm/kernel/asm-offsets.c | 1 +
arch/arm/kernel/entry-common.S | 8 ++++++--
3 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 943ffcf069d2..d8a45c5a1049 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -67,6 +67,7 @@ struct thread_info {
__u32 cpu_domain; /* cpu domain */
struct cpu_context_save cpu_context; /* cpu context */
__u32 abi_syscall; /* ABI type and syscall nr */
+ __u32 sp_syscall; /* SP when entering syscall */
unsigned long tp_value[2]; /* TLS registers */
union fp_state fpstate __attribute__((aligned(8)));
union vfp_state vfpstate;
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 4853875740d0..c9525cbb26b7 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -49,6 +49,7 @@ int main(void)
DEFINE(TI_CPU_DOMAIN, offsetof(struct thread_info, cpu_domain));
DEFINE(TI_CPU_SAVE, offsetof(struct thread_info, cpu_context));
DEFINE(TI_ABI_SYSCALL, offsetof(struct thread_info, abi_syscall));
+ DEFINE(TI_SP_SYSCALL, offsetof(struct thread_info, sp_syscall));
DEFINE(TI_TP_VALUE, offsetof(struct thread_info, tp_value));
DEFINE(TI_FPSTATE, offsetof(struct thread_info, fpstate));
#ifdef CONFIG_VFP
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 3cfc6d952ff9..8baab7f97f59 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -232,6 +232,8 @@ ENTRY(vector_swi)
uaccess_disable tbl
get_thread_info tsk
+ /* Save a per-task copy of SP for sigreturn */
+ str sp, [tsk, #TI_SP_SYSCALL]
adr tbl, sys_call_table @ load syscall table pointer
@@ -377,13 +379,15 @@ sys_syscall:
ENDPROC(sys_syscall)
sys_sigreturn_wrapper:
- add r0, sp, #S_OFF
+ get_thread_info tsk
+ ldr r0, [tsk, #TI_SP_SYSCALL] @ read back SP
mov why, #0 @ prevent syscall restart handling
b sys_sigreturn
ENDPROC(sys_sigreturn_wrapper)
sys_rt_sigreturn_wrapper:
- add r0, sp, #S_OFF
+ get_thread_info tsk
+ ldr r0, [tsk, #TI_SP_SYSCALL] @ read back SP
mov why, #0 @ prevent syscall restart handling
b sys_rt_sigreturn
ENDPROC(sys_rt_sigreturn_wrapper)
--
2.46.2
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