From bffe30dd9f1f3b2608a87ac909a224d6be472485 Mon Sep 17 00:00:00 2001 From: Joerg Roedel Date: Wed, 3 Mar 2021 15:17:16 +0100 Subject: x86/sev-es: Use __copy_from_user_inatomic() The #VC handler must run in atomic context and cannot sleep. This is a problem when it tries to fetch instruction bytes from user-space via copy_from_user(). Introduce a insn_fetch_from_user_inatomic() helper which uses __copy_from_user_inatomic() to safely copy the instruction bytes to kernel memory in the #VC handler. Fixes: 5e3427a7bc432 ("x86/sev-es: Handle instruction fetches from user-space") Signed-off-by: Joerg Roedel Signed-off-by: Borislav Petkov Cc: stable@vger.kernel.org # v5.10+ Link: https://lkml.kernel.org/r/20210303141716.29223-6-joro@8bytes.org --- arch/x86/lib/insn-eval.c | 66 ++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 52 insertions(+), 14 deletions(-) (limited to 'arch/x86/lib/insn-eval.c') diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 4229950a5d78..bb0b3fe1e0a0 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -1415,6 +1415,25 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) } } +static unsigned long insn_get_effective_ip(struct pt_regs *regs) +{ + unsigned long seg_base = 0; + + /* + * If not in user-space long mode, a custom code segment could be in + * use. This is true in protected mode (if the process defined a local + * descriptor table), or virtual-8086 mode. In most of the cases + * seg_base will be zero as in USER_CS. + */ + if (!user_64bit_mode(regs)) { + seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS); + if (seg_base == -1L) + return 0; + } + + return seg_base + regs->ip; +} + /** * insn_fetch_from_user() - Copy instruction bytes from user-space memory * @regs: Structure with register values as seen when entering kernel mode @@ -1431,24 +1450,43 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) */ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE]) { - unsigned long seg_base = 0; + unsigned long ip; int not_copied; - /* - * If not in user-space long mode, a custom code segment could be in - * use. This is true in protected mode (if the process defined a local - * descriptor table), or virtual-8086 mode. In most of the cases - * seg_base will be zero as in USER_CS. - */ - if (!user_64bit_mode(regs)) { - seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS); - if (seg_base == -1L) - return 0; - } + ip = insn_get_effective_ip(regs); + if (!ip) + return 0; + + not_copied = copy_from_user(buf, (void __user *)ip, MAX_INSN_SIZE); + return MAX_INSN_SIZE - not_copied; +} + +/** + * insn_fetch_from_user_inatomic() - Copy instruction bytes from user-space memory + * while in atomic code + * @regs: Structure with register values as seen when entering kernel mode + * @buf: Array to store the fetched instruction + * + * Gets the linear address of the instruction and copies the instruction bytes + * to the buf. This function must be used in atomic context. + * + * Returns: + * + * Number of instruction bytes copied. + * + * 0 if nothing was copied. + */ +int insn_fetch_from_user_inatomic(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE]) +{ + unsigned long ip; + int not_copied; + + ip = insn_get_effective_ip(regs); + if (!ip) + return 0; - not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip), - MAX_INSN_SIZE); + not_copied = __copy_from_user_inatomic(buf, (void __user *)ip, MAX_INSN_SIZE); return MAX_INSN_SIZE - not_copied; } -- cgit v1.2.3