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arm64: Document why we enable PAC support for leaf functions 

Document the fact that we enable pointer authentication protection for
leaf functions since there is some narrow potential for ROP protection
benefits and little overhead has been observed.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20200506195138.22086-2-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Brown 2020-05-06 20:51:28 +01:00 committed by Will Deacon
parent e5159827e0
commit 717b938e22
1 changed files with 3 additions and 0 deletions
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arch/arm64/Makefile
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@ -71,6 +71,9 @@ branch-prot-flags-y += $(call cc-option,-mbranch-protection=none)
ifeq ($(CONFIG_ARM64_PTR_AUTH),y) ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
# We enable additional protection for leaf functions as there is some
# narrow potential for ROP protection benefits and no substantial
# performance impact has been observed.
branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
# -march=armv8.3-a enables the non-nops instructions for PAC, to avoid the # -march=armv8.3-a enables the non-nops instructions for PAC, to avoid the
# compiler to generate them and consequently to break the single image contract # compiler to generate them and consequently to break the single image contract