Commit 9a964285 authored by Will Deacon's avatar Will Deacon
Browse files

arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction 



For better or worse, GDB relies on the exact instruction sequence in the
VDSO sigreturn trampoline in order to unwind from signals correctly.
Commit c91db232 ("arm64: vdso: Convert to modern assembler annotations")
unfortunately added a BTI C instruction to the start of __kernel_rt_sigreturn,
which breaks this check. Thankfully, it's also not required, since the
trampoline is called from a RET instruction when returning from the signal
handler

Remove the unnecessary BTI C instruction from __kernel_rt_sigreturn,
and do the same for the 32-bit VDSO as well for good measure.

Cc: Daniel Kiss <daniel.kiss@arm.com>
Cc: Tamas Zsoldos <tamas.zsoldos@arm.com>
Reviewed-by: default avatarDave Martin <dave.martin@arm.com>
Reviewed-by: default avatarMark Brown <broonie@kernel.org>
Fixes: c91db232 ("arm64: vdso: Convert to modern assembler annotations")
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent e4e9f6df

arch/arm64/include/asm/linkage.h

+3 −3
Original line number Diff line number Diff line
@@ -15,9 +15,9 @@ 
#define BTI_J hint 36 ;



/*

 * When using in-kernel BTI we need to ensure that assembly functions

 * have suitable annotations.  Override SYM_FUNC_START to insert a BTI

 * landing pad at the start of everything.

 * When using in-kernel BTI we need to ensure that PCS-conformant assembly

 * functions have suitable annotations.  Override SYM_FUNC_START to insert

 * a BTI landing pad at the start of everything.

 */

#define SYM_FUNC_START(name)				\

	SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)	\

arch/arm64/kernel/vdso/sigreturn.S

+9 −2
Original line number Diff line number Diff line
@@ -15,7 +15,14 @@ 
	.text



	nop

SYM_FUNC_START(__kernel_rt_sigreturn)

/*

 * GDB relies on being able to identify the sigreturn instruction sequence to

 * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START()

 * here, as it will emit a BTI C instruction and break the unwinder. Thankfully,

 * this function is only ever called from a RET and so omitting the landing pad

 * is perfectly fine.

 */

SYM_CODE_START(__kernel_rt_sigreturn)

	.cfi_startproc

	.cfi_signal_frame

	.cfi_def_cfa	x29, 0
@@ -24,6 +31,6 @@ SYM_FUNC_START(__kernel_rt_sigreturn) 
	mov	x8, #__NR_rt_sigreturn

	svc	#0

	.cfi_endproc

SYM_FUNC_END(__kernel_rt_sigreturn)

SYM_CODE_END(__kernel_rt_sigreturn)



emit_aarch64_feature_1_and

arch/arm64/kernel/vdso32/sigreturn.S

+8 −8
Original line number Diff line number Diff line
@@ -17,39 +17,39 @@ 
	.save {r0-r15}

	.pad #COMPAT_SIGFRAME_REGS_OFFSET

	nop

SYM_FUNC_START(__kernel_sigreturn_arm)

SYM_CODE_START(__kernel_sigreturn_arm)

	mov r7, #__NR_compat_sigreturn

	svc #0

	.fnend

SYM_FUNC_END(__kernel_sigreturn_arm)

SYM_CODE_END(__kernel_sigreturn_arm)



	.fnstart

	.save {r0-r15}

	.pad #COMPAT_RT_SIGFRAME_REGS_OFFSET

	nop

SYM_FUNC_START(__kernel_rt_sigreturn_arm)

SYM_CODE_START(__kernel_rt_sigreturn_arm)

	mov r7, #__NR_compat_rt_sigreturn

	svc #0

	.fnend

SYM_FUNC_END(__kernel_rt_sigreturn_arm)

SYM_CODE_END(__kernel_rt_sigreturn_arm)



	.thumb

	.fnstart

	.save {r0-r15}

	.pad #COMPAT_SIGFRAME_REGS_OFFSET

	nop

SYM_FUNC_START(__kernel_sigreturn_thumb)

SYM_CODE_START(__kernel_sigreturn_thumb)

	mov r7, #__NR_compat_sigreturn

	svc #0

	.fnend

SYM_FUNC_END(__kernel_sigreturn_thumb)

SYM_CODE_END(__kernel_sigreturn_thumb)



	.fnstart

	.save {r0-r15}

	.pad #COMPAT_RT_SIGFRAME_REGS_OFFSET

	nop

SYM_FUNC_START(__kernel_rt_sigreturn_thumb)

SYM_CODE_START(__kernel_rt_sigreturn_thumb)

	mov r7, #__NR_compat_rt_sigreturn

	svc #0

	.fnend

SYM_FUNC_END(__kernel_rt_sigreturn_thumb)
 
SYM_CODE_END(__kernel_rt_sigreturn_thumb)

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